When I was first thinking about becoming a teacher, I looked for books on education in the library. One of the books wasn't so much about teaching as it was about the history of education in America and how it got so screwed up.
Every year, American students prove their inferiority to foreign counterparts.
As I see it, Constructivism is founded on the idea that learners can't just copy what they see, hear, or read into their brains. They have to 'construct' some sort of representation of that meaning it their brain.
This isn't controversial. Psychologists have found good evidence that this is how our memory works.