When a school boasts a class size of 23, that doesn't mean that your student will be in a class of only 23 students. Usually, the class sizes are averaged across the school. That means while one class might have six students in it, another class might have 30. I've had 42 kids in a class in a school whose class size was 25. If you want to know the maximum amount of kids that will be in your student's class, ask about the class cap.