I think the correct form of what you are trying to say would be: "Math seems to be pretty difficult for most other students." (Note that depending on region, one might say "maths" instead of "math." For example, in South Africa I would say "maths," but in Canada I say "math") I believe when you are constructing a sentence involving "difficult," you use "for" if the following term is a noun and "to" if it is a verb. For example, "math is difficult for other students" and "it is difficult to do math." Personally, I would probably word the sentence, "maths seems to be quite difficult for most other students." I personally find it a little more natural to use "quite," but that might just be me ("pretty" would also be much less formal).