The number of students in a class is a time-related idea, a proxy for how much time and attention a teacher can give each student.

In a small class there is more teacher-time available because it's allocated among fewer students. One strategy for improving educational quality is to cut class sizes.

Let's start with the basics. Class sizes in California are abnormally big.

Large class sizes (measured by comparing the number of students to the number of teachers on staff) are nothing new for California. The graph below shows the average "student-teacher ratio" in each state since 1970. This statistic can be used as a proxy for "class size," but it isn't quite the same thing. Most actual class sizes are larger than this statewide benchmark because not all certified teachers working at a school are in classes all day. Still, it is safe to expect that the higher the number of students per teacher in a state in any given year, the larger class sizes must be, and vice versa.

California's student-teacher ratio has been among the highest in America for decades.
More charts like this can be found on EdSource.org at http://bit.ly/mocharts

Clearly, smaller classes cost more than big ones. Does it make a difference?

Yes, Smaller is Better

Like anything in social sciences, context matters. The Center for Public Education (CPE), an initiative of the National School Boards Association, analyzed 19 studies on the subject. They concluded "most of the research shows that when class size reduction programs are well-designed and implemented in the primary grades (K-3), student achievement rises as class size drops."

Importantly, the study concluded that smaller classes produce the greatest benefits for disadvantaged students in grades K-3, and when there are 18 or fewer students per teacher. A research review by the National Education Policy Center (2014) reaches the same conclusion, and analyzes the different research approaches that have been brought to the question.

...the greatest benefits accrue for disadvantaged students in grades K-3, and when there are 18 or fewer students per teacher.

Class Size Matters, an advocacy organization, provides additional information and research on class sizes, including cost-benefit analyses. International comparisons provide additional perspective.

Unintended Consequences

In 1988, California voters passed Proposition 98, which required the California legislature to increase spending on public education. Then-governor George Deukmejian, who had opposed Prop 98, argued that a sudden influx of money would change nothing if it merely raised teacher salaries. As an alternative, he argued that the money should be invested in reducing class sizes for grades K-3, capping class size at twenty students. 

This policy change had a strong basis in research, but it turned out badly. Implemented without a phase-in period, the class-size reduction mandate created a sudden boom in demand for K-3 teachers. As school districts rushed to fill the new teaching positions, experienced teachers had lots of schools to choose from. Unsurprisingly, they tended to choose positions in schools and districts that offered the best salaries and working conditions. Schools serving low-income communities, meanwhile, had a hard time attracting qualified candidates. This dislocation inflicted a lasting and unequal impact on California's schools. The policy serves as a cautionary tale for education reformers: beware unintended consequences.

The California Department of Finance estimates that the state spent over $22 billion on incentives for K-3 class size reduction from the program’s inception until it was changed in 2009-10. In the lean budget years leading to 2013, the incentives were reduced and the rules effectively eliminated. Elementary class sizes rose steadily as a result, keeping California in last position in the country as far as class sizes.

The Local Control Funding Formula, which defines how the state allocates funds to school districts, provides districts about 10% more per K-3 pupil if they either commit to reducing class sizes down to 24 or reach agreement with their teachers’ union for a larger class size. Keen-eyed readers will note that the research referenced above showed a benefit to much, much smaller classes of 18 students or less.

Should Classes Vary in Size?

In virtually any school, the number of students in each class tends to be pretty uniform. Walk into two 4th grade classrooms in a school district at random, and the number of students will probably vary little. Is this uniformity a mistake? Should classes vary in size?

In an influential speech in 2011 Bill Gates encouraged education leaders to re-examine the rationale for maintaining consistent class sizes, arguing that some teachers are better than others at getting results in large classes. "Conservative estimates suggest that we can save more than $10,000 per classroom by increasing class size by just four pupils. If we pay some of that money to our best teachers for taking in more students, we accomplish three goals at once – we save money, we get more students in classrooms with highly effective teachers, and we give our best teachers a real raise, not just for being good, but for taking on more work."

Given the very high student-teacher ratios in California, Gates’ comments could be taken as an argument for reducing class sizes selectively, rather than continuing the uniform K-3 class size approach the state took in 1996. Under the Local Control Funding Formula, which provides extra money for high-need students, local school districts have the power to implement this approach if they want to, for example by reducing class sizes in schools that serve the highest proportions of low-income students or English learners.

School time varies a great deal among the states and around the world. The next lesson takes up the question of how much time students spend learning.

Updated June 2018

Image: Insect Convention CC WoodleyWonderworks