Our district used TERC Investigations for 12 years and it was a huge reason I decided to homeschool my younger son.
I have extensively reviewed the fourth grade TERC books alongside the fourth grade Primary Mathematics (Singapore) and Saxon books. TERC had *far* less practice and the practice it had was with numbers that were "easy." So, fraction problems stuck with halves, thirds, quarters, sixths, eighths, and twelfths whereas the Singapore book had kids dealing with more complicated fractions, like 15ths or 17ths (I'm making these up, but it was like this). TERC had something like five longish division problems in the whole book for the kids to do whereas in Saxon it was up around 100 and Singapore was somewhere in between.
The TERC books I reviewed were an older edition. My understanding is that they came out with something to address concerns about the lack of practice later on.
TERC came to my attention when my younger son was going to be entering kindergarten. When we looked at a well regarded private school for him, they very proudly announced that they used the Investigations program which in kindergarten would be focusing on the number 6. The number 6 for the whole year? Apparently yes. This was my kid who understood place value into the thousands among other things. I knew that wasn't going to work, so I looked at the local public school, thinking that whatever they were using had to be better than that, and that's when I found out that literally *all* of the schools in the area, public and private, were using TERC.
(Sorry for the rant.)
