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Source: Public Policy Institute of California

Class Size Reduction, Teacher Quality, and Academic Achievement in California Public Elementary Schools


Intuitively, class size reduction is a good idea. Parents support it because it means that their children will receive more individual attention from teachers. Teachers like it for the same reason and also because it creates a more manageable workload. It is generally assumed that the fewer students in a class, the better they will learn and the higher they will score on nationwide tests—currently one of the most common measures of student achievement.

Nevertheless, several things could go wrong with mandated class size reduction (CSR). This report presents evidence that the potential success or failure of such a reform may depend largely on how it is implemented and how teachers and administrators respond. If it is implemented quickly on a large scale, such a program may run into serious problems. In the following pages, Christopher Jepsen and Steven Rivkin analyze some of the things that went right and some that did not after California passed its CSR law in 1996.

One problem was the sweeping nature of the legislation, which called for a one-third reduction in class size for kindergarten through third grade in every public elementary school in the state. This resulted in an immediate need for thousands of new teachers. But where were they to come from? And what qualifications would they have? In 1997, the first year after the schools had scrambled to hire new teachers, nearly one-quarter of the teaching workforce in California had one year of experience or less.

The authors also point to a more serious problem. Many teachers in economically disadvantaged communities left their schools to fill vacancies created in other schools. Thus, many schools had to fill not only the positions created by their own efforts to reduce class size but also positions vacated by departing teachers.

The analysis reveals that the effects of class size reduction extended beyond the third grade, leading to lower achievement in the fifth grade among schools with a high percentage of black students. Evidently, many fourth- and fifth-grade teachers chose to move to the earlier grades with fewer students, leaving many schools with the need to hire new teachers in other grades as well as K–3. In fact, the analysis indicates that schools that had trouble hiring experienced teachers before CSR are the very schools that did not appear to benefit from CSR.

On the positive side, the authors find that, all else equal, smaller classes raise student achievement. Reducing class size by 10 students raises the percentage of third-grade students who exceed national median test scores by about 4 percentage points in mathematics and 3 percentage points in reading. However, all else is not equal when you hire thousands of new teachers. Separating out the effects of new teachers from the effects of smaller classes, Jepsen and Rivkin find that having a new teacher reduces the percentage of students who exceed the national median by roughly 3 percentage points in both mathematics and reading. So in many schools, class size reduction has meant zero gain, at least in the short run.

The bottom line is that California has implemented a $1.6-billion-ayear program that is apparently yielding only modest gains. It also appears that some students and schools have actually been hurt rather than helped by class size reduction.

And now the cost of the reform is becoming a problem itself. California implemented CSR during prosperous times, when it had a strong budget surplus. The state also picked up most of the cost. Today, California is suffering from a $20 billion shortfall, and school districts find themselves shouldering more of the fiscal burden. Faced with difficulty in meeting essential costs, such as teacher salaries, maintenance, and materials for the classroom, some districts are choosing to leave the program, preferring larger classes to cutbacks in other areas.

CSR does not appear to have been the silver bullet many expected it to be. If it remains in place, one obvious policy response at this point would be to help beginning teachers adapt to the classroom more quickly and effectively and gain the essential training they need. An ongoing concern that also needs to be addressed is the large disparity across schools in teacher qualifications and student achievement. There is sufficient evidence to suggest that improving the quality of the teaching staff in any school will go a long way toward improving student achievement.

According to the authors, another lesson that other states might learn from the California experience is this: “A better approach to class size reduction would have been to reduce class sizes in a subset of schools each year, starting with low-performing schools serving high-poverty populations. This would have limited the departure of teachers for newly created jobs in suburban schools, lessened the overall competition for new teachers, and reduced inequality in academic performance.” No single reform will improve California’s K–12 system. As we have learned from the class size reduction program, unintended consequences can offset gains as well as create whole new problems. Much can be learned, however, from incremental policy changes for a limited number of school districts before scaling up to statewide implementation. There is much still to be done, and the lessons from CSR will make the next steps more informed.

David W. Lyon President and CEO Public Policy Institute of California


In response to widespread dissatisfaction with the public schools, California has implemented a number of educational reforms over the past decade. Perhaps the most dramatic, and certainly the most costly, was the passage of the class size reduction (CSR) law in the summer of 1996. This legislation aimed to reduce average class size in grades kindergarten through third grade by roughly one-third, from 30 students to 20, at an annual cost of over $1 billion.

Educators and policymakers were hopeful that the gains attributed to smaller class sizes in an experiment conducted in Tennessee would translate into large gains in achievement following California’s statewide class size reduction. However, the hiring of large numbers of inexperienced teachers in response to CSR had the potential to offset the direct benefits of smaller classes, particularly for schools in economically disadvantaged communities that had extreme staffing difficulties before class size reduction.

Because test scores before CSR are not available for most schools, the total effect of CSR will never be known. However, this report attempts to provide some limited but very important answers to the following questions:

  1. What were the effects of CSR on teacher experience, certification, and education? Were some schools affected more than others?
  2. How did CSR affect student achievement in third grade? What were the benefits of smaller classes? What were the effects of new teachers?
  3. Are the benefits of smaller classes concentrated among a subset of students, or did all schools benefit equally from CSR? For example, many researchers find that low-income and nonwhite students benefit more from smaller classes than do other students.

Student Diversity

Immigration and other factors led to substantial demographic changes in California public elementary schools during the 1990s. No single ethnic group constitutes a majority of students: However, Hispanics are the most populous group. At the same time, large percentages of students are attending schools where more than half the student population is enrolled in free or reduced-price (i.e., subsidized) lunch programs. There are substantial differences across the state in the distribution of students by race/ethnicity and by the percentage enrolled in subsidized lunch programs. For example, urban schools have higher percentages of nonwhite students and low-income students than do suburban or rural schools. Such differences in demographic composition, even among the largest districts in the state, raise the possibility that CSR may have had dramatically different effects across the state, depending largely on the strength of the relationship between teacher characteristics and student demographic composition.

Teacher Characteristics

Numerous reports have documented the change in teacher characteristics following the implementation of CSR. Although our description of California elementary school teachers covers much of the same ground as earlier work, there are several key additions. First, rather than combining all teachers with less than three years of experience into a single category, we create separate categories for first- and second-year teachers and group all remaining teachers with at least two years of experience into a single category. Second, earlier studies examined differences in teacher characteristics by community type, student racial/ethnic composition, or student income, but they did not consider the distribution of teacher characteristics for combinations of these factors. As the distribution of students within each subsidized lunch category (0 to 25 percent, 25 to 50 percent, 50 to 75 percent, 75 to 100 percent) differs by race, the distribution of teacher characteristics likely differs as well. However, these teacher differences would be overlooked if one were focusing solely on either race/ethnicity or income categories.

CSR led to a dramatic increase in the percentages of inexperienced and uncertified teachers. In 1990, there were few differences in these characteristics by racial/ethnic and income groups. Even as late as 1995– 1996, the year before CSR, schools with high percentages of nonwhite and low-income students were slightly more likely than other schools to have inexperienced teachers who lacked full certification and postgraduate schooling. By 1999, large gaps in teacher qualifications emerged between schools attended by nonwhite and low-income students compared with other schools. For black students in schools with more than 75 percent of the students enrolled in subsidized lunch programs, nearly 25 percent had a first- or second-year teacher; almost 30 percent had a teacher who was not fully certified. At the other extreme, for white students attending schools with 25 percent or less of the students enrolled in subsidized lunch programs, only 12 percent had a first- or second-year teacher, and only 5 percent had a teacher who was not fully credentialed. These differences reflect the varying level of difficulty that many schools experienced in attempting to attract and retain teachers following the implementation of CSR.

Student Achievement

Evaluating the effect of CSR on student achievement is challenging for a number of reasons. First and probably most important, there are no statewide test scores in the years immediately preceding the implementation of CSR. Statewide tests began in 1997–1998, the second year of CSR. Thus, although much can be learned about the costs and benefits of CSR, its total effect on achievement will never be known.

Second, not all schools were able to participate in the program immediately, probably because of shortages of space and qualified teachers. Because participating schools had to reduce class size in first and second grade before reducing class size in other grades, adoption of CSR in the first and second grades was nearly complete by 1997–1998. Therefore, it is nearly impossible to compare achievement in 1997–1998 of schools that implemented CSR in these grades with ones that had not implemented CSR. However, nearly one-third of the schools had not implemented CSR in third grade as of 1997–1998. Consequently, it is possible to compare achievement in schools that reduced class sizes in third grade to achievement in those that had not.

The decision to implement CSR is not random but is based on financial or space constraints or a lack of qualified teachers. These factors also affect student achievement, making it extremely difficult to separate the effects of these constraints from the effects of CSR. The state-supported CSR Research Consortium has attempted to control for these differences between schools, but it is not clear that the consortium completely controlled for these between-school differences in its analysis of achievement.

Rather than looking at changes between schools, our analysis examines changes within schools in average class size in third grade between 1997–1998 and 1999–2000. We measure the effects of these changes, along with changes in teacher characteristics, on third-grade mathematics and reading achievement in California. This technique allows us to consider two effects of class size reduction on student achievement: the effects from the reduction in class size and the effects from the change in the teacher force. One main finding of Tennessee’s Student/Teacher Achievement Ratio (STAR) experiment was that, all else equal, smaller classes are associated with higher achievement. In California, though, all else was not equal. As noted above, there were dramatic changes in teacher characteristics following the reduction of average class size, particularly for nonwhite students. This increase in the number of inexperienced and not fully certified teachers is to be expected when hiring a large number of new teachers. The effects of these increases should disappear as these new teachers acquire experience and full certification.

However, CSR likely had a more profound effect on the teacher workforce than simply increasing the number of inexperienced and uncertified teachers. Thousands of additional teaching positions were created, but thousands of additional teachers were not. Therefore, much of the increase in teachers consists of individuals who would not have been hired as teachers in the absence of CSR, especially given the availability of jobs with better pay and working conditions. If these teachers continue to be of lower quality than other teachers even after they have acquired additional experience, certification, or education, then CSR has the potential to create a long-term reduction in teacher quality. The analysis shows that a ten-student reduction in class size (the average under CSR) raises the percentage of third-grade students who exceed the national median test score by roughly 4 percentage points in mathematics and 3 percentage points in reading. These findings are slightly larger than the effects found by the consortium in its analyses. Unlike the consortium, we find substantial variation by school in CSR’s effect on achievement. Schools with more low-income students likely receive larger benefits, whereas schools in rural areas and those in which a high proportion of the students are black (primarily in Los Angeles Unified School District) appear to benefit little if at all from smaller classes.

The relationship between teacher characteristics and achievement is much weaker. The only indicator that is systematically linked to student achievement in third grade is experience. Having a new teacher reduces the percentage of students who exceed the national median by roughly 3 percentage points in both mathematics and reading. There is little or no evidence that teacher education or certification is significantly related to student achievement in third grade. However, the finding for certification could be influenced by the lower quality of the certification data.

One possible explanation for the variation in class size effects is the timing of CSR. As mentioned above, nearly one-third of schools had not implemented CSR in 1997–1998. The results show that for schools with a large percentage of black students, those recently implementing CSR have much smaller benefits from class size reduction than do other high-percentage black schools. A similar result is found for rural schools. In contrast, there is little evidence of a difference in class size benefits based on CSR timing in schools serving predominantly middle-class, nonblack students.

However, the hiring of new teachers explains only a portion of the difference in class size effects by CSR timing. Recent research in Texas and elsewhere has documented that hard-to-measure teacher attributes have an important effect on student achievement. It is likely that the smaller effects of class size for recent CSR implementers are related to changes in these hard-to-measure components of teacher quality, given that they are related to easier-to-measure teacher attributes such as experience. The schools that do not appear to benefit from CSR are the same schools that had trouble hiring experienced, certified teachers before CSR.

The estimated decline in third-grade teacher quality in this analysis probably understates the actual quality decline that accompanied the implementation of CSR statewide in two ways. First, the effects of class size reduction on teacher quality extend beyond the grades where class sizes were reduced. An analysis of fifth-grade achievement shows that class size reduction in third grade is negatively associated with achievement in fifth grade for schools with a high percentage of black students. Such a finding is consistent with the story that the movement of many fourth- and fifth-grade teachers into the early grades meant that schools had to rapidly expand hiring in all grades, not just K–3. Second, and perhaps even more important, the available data are not able to capture between-school changes in instructional effectiveness. Yet, it is widely believed that many teachers switched schools as a result of class size reduction. Schools must fill not only the additional positions created by their own efforts to reduce class size but also positions vacated by the departure of teachers for newly created opportunities at other schools.

Policy Implications

Because it is difficult to calculate the magnitude of the benefits of CSR in terms of higher student achievement, the question of whether money would have been better spent on other aspects of schools such as higher teacher salaries, expanded and improved pre-school, technology, or other programs is very hard to answer. Nevertheless, there is clear evidence that, controlling for changes in teacher quality, smaller classes raised student achievement and the effects were larger in schools serving predominantly lower-income students. Unfortunately, these schools tended to suffer the largest deterioration in teacher quality as measured by experience and certification. A better approach to class size reduction would have been to reduce class sizes in a subset of schools each year, starting with low-performing schools serving high-poverty populations.

This would have limited the departure of teachers for newly created jobs in suburban schools, lessened the overall competition for new teachers, and reduced inequality in academic performance. The results concerning new teachers and their struggles highlight the importance of policies targeting new teachers, such as the Beginning Teacher Support Act (BTSA). These types of programs have two potential benefits. First, they can minimize the adverse effects of new teachers by helping them adapt to the classroom more quickly and effectively. Making these teachers more productive and effective also reduces the stress of the job, thereby reducing teacher turnover. Effective programs that assist new teachers will become even more essential in the near future, as enrollment and teacher retirements both increase. Future research should carefully analyze the effectiveness of programs such as BTSA on student achievement.

Although we find that experience matters, the relationship between certification and achievement is much less clear. Our results show that California’s certification system in the late 1990s had little if any relationship to student achievement, suggesting that policies that prevent uncertified teachers from teaching are unlikely to raise student achievement. The concern about the weak relationship between certification and student achievement is well known to California policymakers, and the California Commission on Teacher Credentialing (CCTC) is currently reforming the certification process. It is hoped that the effect of these reforms will be studied rigorously.

At the same time, the available data in California on certification limit the inferences that can be drawn. For example, it is not possible to distinguish between the two types of full credentials (preliminary versus professional clear). Nor can the data from the CCTC be linked to the California Basic Educational Data System (CBEDS) from the Department of Education. It is not possible to match individual student test scores from one year to the next to measure student growth. Thus, several improvements to the current data collection system are needed to conduct an in-depth evaluation of the effects of certification on student achievement.

Here is another CSR Study by WestEd.

Santa Ana orders class-size program audit

The district, accused of creating phantom classes and misusing substitutes to qualify for state funds, seeks outside review

By Seema Mehta, Los Angeles Times, March 29, 2007

Independent auditors will examine Santa Ana Unified School District's class-size reduction program, an investigation prompted by a Times report that the district falsified documents and misused substitute teachers in an effort to retain state funding earmarked for small kindergarten through third-grade classes.

While the district will pay for the audit, the state and county departments of education, which oversee the class-size reduction program and the district's finances, respectively, will monitor the results.

"I'm extremely concerned," said Jack O'Connell, the state superintendent of public instruction who wrote the class-size reduction legislation in 1996 as a member of the state Senate. The legislation calls for an average ratio of 20 students per teacher in each classroom. "This appears to be contrary to the intent of my bill and our law."

In the current school year, 54,800-student Santa Ana Unified was expected to receive about $16 million in additional funding through the class-size reduction program, which was designed to help schools maintain small classes in kindergarten through third grade, according to the California Department of Education.

A Times article published Wednesday recounted how the district's attempt to meet the 20-students-per-teacher cap resulted in the creation of false class rosters and the misuse of substitute teachers. The crowded classrooms were caused, in part, when class sizes hadn't shrunk as expected.

The situation came to light after eight teachers at Washington Elementary School were alarmed by requests to sign attendance rosters that omitted several of their students.

Documents revealed that school officials created a fictitious second-grade roster of students in a class that didn't exist. The phantom classroom diluted the number of second-graders in existing classrooms — allowing the average class size to fall below 20.5 and giving the district an additional $1,024 per student per year.

A substitute teacher was assigned to the nonexistent class, but several teachers at the school said she spent only a few hours over the last month in each classroom instructing students on her roster. District officials said this week that the problems were caused by a shortage of substitute teachers who were supposed to "team teach" with full-time teachers.

State officials contacted the district Wednesday about The Times' story, and were told that district administrators planned to launch an audit by an independent firm. Attempts on Wednesday to reach Santa Ana Unified administrators about the audit, its scope, cost and timeline were unsuccessful.

On Wednesday, the district released a statement that said it would address teachers' concerns and conduct an audit. It also said that "at no time have false rosters been submitted to the state."

At a meeting Wednesday afternoon at Washington Elementary, district officials told about 45 teachers and staff that the district would correct attendance rosters to accurately reflect the number of students that were in teachers' classrooms, according to a teacher who attended the meeting and asked not to be identified for fear of retribution.

The class-size reduction documentation is due to the state May 4, said Lynn Piccoli, who runs the $1.8-billion class-size reduction program for the California Department of Education.

The district has already received $4.3 million of the $16 million it expected to receive this year in class-size reduction funds. The remainder normally would have been released this summer, Piccoli said.

Santa Ana's share of the funds will depend on what the audit reveals, said Piccoli, who added that she had never encountered such allegations. "This is new territory," she said. "It's still very early. Right now, it's kind of wait and see."

Board members, who were briefed about the allegations Tuesday, said it's important that the district comply with state guidelines.

"We want to make sure that folks are following the rules as they're laid out," said board President Rob Richardson. "If the practices were more widespread than one school, we need to know that and take steps to correct it, and we will."

Board member John Palacio questioned if there were other instances of administrators allegedly manipulating data to increase revenue.

"I do not support the district administration asking our employees to alter public documents in order to receive extra public funds," Palacio said. "This is mismanagement of public funds and fraud…. We are also cheating our students in the classroom whose parents are being misled into believing that classes are being made smaller to improve academic performance."

But board member Audrey Yamagata-Noji countered that she thought any missteps were the result of good intentions that went awry.

"I would not categorize this as an intentional act to create phantom classrooms to rip off the state," she said. "Our understanding of what was acceptable probably faltered in some of our oversight. I also am unsure of whether this is rampant across the district; this may not be. It was all done for the right reasons: to try to keep class size down and to keep as much teacher-to-student attention as possible."

Yamagata-Noji was among several district officials who said this week that they wished the teachers would have approached school or district staff or trustees with their concerns, rather than the media.

Union President David Barton characterized such statements as disingenuous.

After receiving calls from concerned teachers in four district schools, Barton said he asked district officials more than two weeks ago to provide a legal justification for the practice and has yet to receive a response. He said the union plans to consult its attorneys about the matter.


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Last modified: November 12, 2004

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