I am also in a moment of deep thought about my belief in constructivism, particularly in math and most particularly in the Middle School age range.
I watch, year after year, how my students superficially work with the algebra models I present them, such as algebra tiles, and then quickly disassociate from these model when they start doing "real algebra" (moving letters and numbers around is "real" to them, and to society as well).
The more I learn about Singapore math, the more intrigued and questioning I am about this model of math education. It isn't constructivist, as I understand, to present the students with exclusive models to think about, but on the other hand, it is through these models that the students often DO "construct" their understanding. Maybe I've been adhering to a very pure understanding of constructivist theory that is divorced from the reality of real learners.