can a swede on a student visa leave china and re-enter on the same student type?

Which specific type do you have, S1 or S2?
If you have a S1, you need to change it to a resident permit after you enter China. Then you can use the permit to enter and re-enter China as many time as you want.

If you have a S2, usually, it is a single entry and you cannot leave and re-enter.