The children in my elementary school classes were curious and asked questions. In a biology lesson in which some sort of beetles were raised from larva, every student was -fascinated-. These same students, three years later (discontinuity after that point - I changed school districts), were bored speechless by dissections, and wouldn't even answer questions, much less ask them, in lessons.

It was a lot more obvious to me, because I typically dropped out of public education less than halfway through the year, bored. So the changes weren't slow and subtle - I'd come back with the new school year, and the students would be noticeably more apathetic.

I don't know for certain that the apathy translated into reduced critical thinking skills, but certainly they weren't using them in the lessons anymore.