Bigger classes mean more work for the teacher and there are only so many people one person can teach successfully like if you have a 50 student class and 20 students are having trouble that is going to be alot and you also have more kids asking questions. You also need to relax from time to time but with too many students it's imposible and normal students won't do as good on their test as if there were less people.
Larger class sizes can make it harder for individual students to learn. It limits the one-on-one time that the teacher can have with each student. Not only that but because there are more students that the teacher may have to stop and help, there is less time in class to cover content. Less time to cover content leads to more homework and more stress on the students that do not understand what did not get covered in class.
