The problem is that critical thinking is essentially a negative activity. It's a means of defending oneself against potentially harmful ideas or ideas that one

The problem is that critical thinking is essentially a negative activity. It's a means of defending oneself against potentially harmful ideas or ideas that one simply doesn't like. It's also rather abstract. One can't learn to think critically until one has learnt to think. One can't learn to think at all until he has first learnt some ideas to think about. To engage the human mind (and the human heart) one needs something positive to aim for. That's why I think that the best approach is not to pick and choose among ideas and then make certain subjects compulsory (as in a curriculum). Rather find something that interests a child and then figure out how to do more of it. But this is best pursued outside the school system.