I feel that students are becoming stronger math students by using CPM textbooks. They have a better understanding of the concepts behind the mathematics rather than just plugging numbers into formulas and trying to cookie cut ever problem into similar type problems.
It is great to see the "ah ha" moments on their faces as we solve problems. It is also great to hear them say, "Oh, I totally get this…it totally makes sense. I love this stuff. I actually like math now."
I love guiding the questions to make students go back and really look at the math involved in the problem and how they can successfully solve a pretty tough "big problem."