Question

A teacher wants her students to tackle challenging tasks. the best strategy is for the teacher to praise her students: for being such wonderful kids. by giving out rewards for getting "a"s. for being so smart. when they work hard.

Answer 1

I believe the answer is: when they work hard.
In this situation, the teacher need to realize that there is always a potential of failure when people are trying to solve challenging task.
So, the teacher need to prepare the students to stay positive under such situation as long as they've given their best effort.