When I first heard of Math-U-See, I have to admit the name was a bit off-putting. To me it sounded childish and unprofessional. I can assure you, though, this curriculum is anything but those things. In our 8 years of homeschooling, this is the only subject in which we haven't changed curriculum.
I'll start my review with the cons:
1. The name. I'm sorry, but it still bothers me.
2. I had a lot of trouble finding testimonials about upper-level testing success. I even made a plea on the MUS Facebook page and another highly populated homeschooling support site. But after much research and prayer, I decided not to switch before the middle school years. When I was questioning my choice of curriculum -- as any over-thinker would -- I talked to my father and brother, both successful engineers (aeronautic and chemical respectively). They both said if a math program is teaching the basic concepts, it's fine. I took great comfort in that and we carried on. I don't regret that decision.
