Instead of changing the background color, can you print on appropriately
colored paper instead? That's generally how people change background colors
in Word.
You can put a rectangular autoshape in the header of the Word template to
create a colored background, but, assuming that you are printing these at
school, you (more than likely) won't be able to print clear to the edge of
the page, so you'll end up with a white border -- and the white border may
not be equally sized on each of the page edges. We run into this in the
PowerPoint newsgroup all the time. See Margins are wrong, printout is
off-center, I don't want any margins
http://www.rdpslides.com/pptfaq/FAQ00097.htm for an explanation of why this
is so.
If you're printing with a service bureau or professional printer, whether
they can go edge to edge will depend on what device they're printing/copying
on. If they have to trim, it will probably cost you a little more.