Are you using diffrent word processors?
If the school and yourself are using diffrent Word versions it has to convert from your version to theirs and vice versa.
If your using 2007 and they are using 2003, you would have to save the file in the older format in order for the file to be read by the school computer.
If they are using 2007 and your using Word 2003 usually it will not read it unless you install a patch from the microsoft website to have it open docx files.
It is very unlikely your using a Word version as old as 2.0, 6.0, 95 or 97.
Each Word version acts in a slighty diffrent behavior, as in margins, text etc.