@bojans congratulations on your son making it to nationals in Boys 1, that is terrific!
@Bruce_Butterfield is exactly correct above. if you watch the ski, the air is great, but the ski never gets around to 180 degrees, so that is why he isn't getting credit for the trick. Its the same thing with his reverse back. Has he tried the "full back" where he lets go of the handle and reconnects behind his back? Its a little slower for now, but he has plenty of time in his run, and that is a good way to learn it and that is almost always credit. Again as Bruce said, learning outside the wake is the best way to do it.
Also just a little note, make sure he is careful on those sideslides too. There is to be a pause between each trick and he certainly flies from one to another. Don't want him to lose credit on those when he has time in his run.
Hope that helps!