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Class size is always a hot topic, especially among parents and teachers.
According to the National Center for Education Statistics , in the 2011-2012 school year, average class size across all public schools in the United States was 21.6 students in elementary school, 25.5 students in middle school, and 24.2 students in high school. This month, Teacher Trendline looks at class size restrictions and what happens when class size limits are exceeded.
Class size restrictions
Among the 149 districts in the database, 102 explicitly mention some form of class size restriction in collective bargaining agreements or board policies. The majority of these set absolute or targeted maximum class sizes, although the language often excludes some grades. Among the districts that do set limits, a little over half (57 districts) have limits for all grades from kindergarten through grade 12.
When districts limit class size, on average they set the limit of about 20 students in pre-kindergarten. At the secondary level, the limit is much higher at an average of about 31 students in a 12th grade class. 
The table above doesn't include districts that aren't mandating or suggesting a cap to class sizes but try to control class sizes in other ways, such as defining the average class size or setting school- or district-wide student to teacher ratios. These policies give districts more flexibility in staffing decisions. In Mesa (AZ), for example, the goal for the average K-3 class size at each school is 26 students.
Districts are much less apt to set limits for secondary grades than elementary grades. While 92 districts set limits for kindergarten, only 60 districts set them for 12 th grade, generally expressing more flexibility about class sizes for older students. For example, Buffalo and Jefferson County (CO) limit secondary class size by specifying a limit on the number of students taught throughout the day (120 to 150 students in Buffalo, 150 students in Jefferson County).
When districts do set class size limits in secondary grades, it's not uncommon for these limits to vary depending on the subject being taught. Fourteen districts reference different class size limits for academic or core classes and non-academic classes or electives. For example, in secondary grades in Cincinnati, academic classes are capped at 30 students while elective classes are capped at 34 students.
There are six districts that vary class size restrictions based on the demographics of the students in the school. In New York City, class sizes are smaller in middle school grades in Title I schools. St. Paul has lower class sizes in all grades for high-poverty schools. Minneapolis only specifies class size maximums for high-poverty schools. Several California districts, including Los Angeles, Sacramento, and Oakland, also set lower class size restrictions for high poverty schools.
Four districts (Montgomery County (MD), Baltimore City, Philadelphia, and Greenville County (SC)) are particularly flexible, allowing class size to vary each year depending upon budget and student needs.
Exceeding class size limits
Even with the best of intentions, sometimes districts exceed class size restrictions . In fact, it is not unusual to see language in class size policies referencing class size "targets" or "goals" (as opposed to fixed caps), essentially statements that the district will make an effort to meet the goals outlined in the policy, but if it is necessary to exceed the target, a school has permission to do so. While half of the districts are silent as to consequences when targets are exceeded, half (72 of 149) do spell out what the consequences must be.
The most common consequence is that the school must add a paraprofessional or teacher's aide to the class. Contracts also often stipulate that parents must be notified as well as holding a meeting between the teacher and the administration to discuss solutions.
There are several districts, counted in the "Other" category above, that explicitly say that the class size limit must be kept at any cost. In Long Beach, a return to the cap is required within 20 days. In Santa Ana (CA), the district must correct a K-3 class size variance within three weeks. In Columbus (OH), the district must reduce the class size, unless the teacher agrees to exceed the limit. Other districts in this category have policies to reduce teachers' non-teaching duties ( Boston, Minneapolis) or give teachers additional preparation time ( Santa Ana, Chicago, Minneapolis).
In districts that offer compensation to teachers for exceeding class size limits, the amount of compensation is usually determined by a formula that involves a rate of pay per student over the limit for a given amount of time. For example, in Santa Ana intermediate and high school teachers make $10 per student over the limit per day. Other districts have greater variation. In Corona-Norco (CA), teachers in grades K-8 received $500 per semester while teachers in secondary grades receive either $600 or $1000 per semester depending on the number of students over the daily student limit. In Toledo, teachers receive $125 per student per instructional hour in elementary grades or per period in secondary grades.
There are six districts with policies that allow teachers to address their class size concerns, even though their contracts do not actually specify the size of classes. Prince George's County(MD) and Bismarck (ND) describe only in general terms that the district will take action if class sizes are deemed to be a problem, but in Portland (OR), Christina (DE), Red Clay (DE), and Alpine (UT), teachers are directed to appeal a class size problem to their supervisors.
An international comparison
The Organization for Economic Cooperation and Development gathers data on a variety of education-related topics, including average class size , for its member countries. The graph below shows how class sizes in the U.S. compare to those of 32 other countries. I n elementary grades, the U.S. has a slightly lower than average elementary class size across these countries. The international average elementary class size is 21.95 while the average elementary class size in the U.S. is 21.5. In middle school, the U.S. average class size is 27.6, roughly three students higher than the international average of 24.3.
Access all of our data on class size policies and more by visiting the Teacher Contract Database .
The Teacher Contract Database includes information on over 145 school districts in the United States: the 60 largest districts in the country, the largest district in each state, the member districts of the Council of Great City Schools, and districts that won the Broad Prize for Urban Education. The database features answers to over 100 policy questions and provides access to teacher contracts, salary schedules, and board policies in addition to relevant state laws governing teachers.
 In some districts, limits vary by subject or school demographics. In these cases, we used the limits set for core academic classes and/or schools that were not high needs or participating in special programs.