You did not mention which version you are using in your school. If you are using the creative cloud version then in order to use it you can but the Education version of Creative cloud or just indesign.
Are you saying that you cannot open the files you've saved at school? If the school uses CS3 you can export the files (at school) to .inx (InDesign Interchange Format), and that should open, with potential missing features and text reflow, in a fully updated CS2, but there is no way to go from later versions to CS2 without passing through CS4 and CS3, and your files likely would be a mess if you tried.
The bottom line here is that CS2 is six versions out of date and you should use the same version as your school. Do they not have some sort of lab you can use after class?