I have had the good fortune of observing three of my daughters learn math using Investigations. Two of them are now in middle school, thriving in math, as a result of the foundation laid in elementary school.
I graduated from Stanford, earning a degree in civil engineering in the mid-1970's. I was always successful at math, but never learned it or developed a feel for what it meant in the way that my daughters are now. I am relieved that they are being educated at this time when reformed math curriculae like Investigations are available to their classroom teachers.
After working as a civil engineer, I recently returned to school to earn a teaching credential. I now am teaching high school math at a low achieving high school in Portland. I can spot the students who have some depth of understanding of mathematical patterns and number sense. Generally there's some standards-based curriculum in their background. When I see it, I am relieved for them. Not angry. Not worried. Not frustrated with opportunity lost. Quite the contrary. When I see a students who has had teachers who moved away from the abstract to the meaningful, I see hope for that student's future.
We parents come with a variety of perspectives. Don't presume we all want what we had in the way of math curriculum or instruction for our children. I certainly do not.