I'm a rookie here who coaches a AA Little League team here in SoCal (9-10 year olds). My son is 9 and this is his 2nd year pitching and he experienced this exact problem. My wife videotaped him in the first game and we went out to the practice field the very next day, as he was trying to throw so hard "over the top" that he had to jerk his head out of the way for the ball to get past him. Consequently he lost all vision of the strike zone and was wild.
The first thing I did was try to have him keep the ball from going too far behind his back, and I did that by having him keep his glove closer to his body and by having him not bring the ball so far down...just bring it back, up, and out.
For the throwing motion itself, I used clock terms...he was trying to throw it at 12:00, so when I see him start to jerk his head, I just holler out "One O'Clock, Two O'Clock" and it triggers him to let his arm go more natural in a 3/4 position. Last outing was 3 1/3 innings in 50 pitches with 8Ks and only 1 hit...I'll take that! Now that it is under control, we will work on a bigger hip rotation and longer stride.