How bout good first grader position is to prevent people from resting their upper body weight on their hands (bad positioning)? I've seen a guy shaking out his hands in class because he did that.

I was actually explained the two other positions:

Standing position 2 - again no resting your weight on the handlebars, you keep your stance with your leg muscles.

also, our trainer says to round your back sometimes in pos. 3, standing, to work your glutes.