In Three Things to Unlearn from School, Ben Casnocha cites Bill Bullard's list of three bad habits of thought: Attaching importance to personal opinions, solving given problems, and earning the approval of others. Bullard's proposed alternatives don't look very good to me, but Bullard has surely identified some important problems.

I can think of other school-inculcated bad habits of thought, too many to list, but I'll name two of my least favorite.

I suspect the most dangerous habit of thought taught in schools is that even if you don't really understand something, you should parrot it back anyway. One of the most fundamental life skills is realizing when you are confused, and school actively destroys this ability - teaches students that they "understand" when they can successfully answer questions on an exam, which is very very very far from absorbing the knowledge and making it a part of you. Students learn the habit that eating consists of putting food into mouth; the exams can't test for chewing or swallowing, and so they starve.