You didn't say what level you teach. I assume we're talking PC's here since
you mentioned CorelDraw (although CorelDraw does have a Mac version). For
scanned photo manipulation you want to use the term "paint software". The
Corel program you are probably referring to is PhotoPaint. It comes bundled
with a lot of HP scanners. PhotoPaint is a good program once you travel up
the steep learning curve. Not a program for much below H.S. kids, IMHO.
Corel Xara also fits into this category.
But, a new program which we got over the holidays is a gas to use with
almost any age kid - GOO by Kai's Power Tools. It is well worth the $49.00
cost, fun and easy to learn. This may not be the most serious art tool, but
if you want to turn kids onto computer graphics as an introduction, this
program can't be beat.