<p>Schools may report an average class size that is a simple average of the sizes of all of the classes at the school.</p>
<p>However, that may not give a true reflection of the class sizes that students experience. This is because larger classes are larger, so they will be weighted more in student experiences.</p>
<p>Here is an example: Suppose a college with 100 students per class level requires 4 courses to graduate, 1 each year. The first 2 are required for everyone, and taught in 100 student classes. The last 2 are chosen from 10 junior electives and 10 senior electives, each taught in 10 student classes.</p>
<p>A simple average gives (100 * 2 + 10 * 20) / 22 = 18.2 students per class on average, with only 9.1% of classes being larger than 10 students.</p>
<p>However, each student experiences 2 classes of 100 students and 2 classes of 10 students. Each student therefore experiences (100 * 2 + 10 * 2) / 4 = 55 students per class on average, with 50% of classes being larger than 10 students.</p>