I didn't get a really aggressively stupid teacher (or, at least, one I realised was that stupid) until I was 12. I worked out (I think) 37 times 4 in my head (it was thirty-something times an integer less than five) and he looked at me like I was a suspicious freak who was up to something for having been able to do this in my head and not consider it remarkable. I shudder at the thought that that was ever in charge of children.
A Slate article by psychologist Alison Gopnik about how preschoolers have already learned to accept what the teacher says rather than exploring things to develop their own understanding:
This experiment is from:
D. Buchsbaum, A. Gopnik, T.L. Griffiths, and P. Shafto (2011). Children's imitation of causal action sequences is influenced by statistical and pedagogical evidence. Cognition (in press). pdf
The other paper cited in the Slate article is:
E. Bonawitz, P. Shafto, H. Gweon, N.D. Goodman, E. Spelke, and L. Schulz (2011). The double-edged sword of pedagogy: Instruction limits spontaneous exploration and discovery. Cognition (in press). pdf