I have had excellent results with both my 5th and 2nd Graders doing MUS. I use MUS for their math core, then I add Calculadder for drills as the concepts are presented in MUS. I also have them each do one page in a Miquon Math Lab daily- this is their "fun" math, and it really teaches them to think outside the box. We just had the 5th grader tested, and he tested into high school. Before the test, I was thinking about switching to a 'real' math curriculum for 5th grade, like Saxon, etc. But if it isn't broken don't fix it!