Both PER and FOR are prepositions which can be used in this phrase. However, it depends on what you’re trying to say.
The most likely answer is “I have 10 students per class”.
This means that for each class that you hold, there are 10 students who attend.
PER means two things.
- For each. Used in this case, because you are saying that for each class you have, there are 10 students.
- The way something is done. For example, “I sent you a memo per bike messenger”.
FOR can mean many things. Here are two common uses.
- To illustrate purpose.
Example: “I have glasses for reading”. - To show an exchange.
Example: “I’ll give you my chips for your chocolate bar”.
When saying “10 students for class” it shows that there were 10 students who were there for the purpose of having a class. In that case, I could say “10 students came for class today”.
