Quarterback release

Coach, I would suggest you remind your QB of one distinction he needs to make in order to heighten his release - he must understand the proper height of the elbow for effective throwing and why it's important. The sidearm throw is a function of his elbow passing below his shoulder line on the turn and the elbow is supposed to "lead" the throw for everything to work right. Physically speaking, remind him that it is functionally impossible for the elbow to "lead" the throw(meaning get ahead of the wrist in the release), if it does not pass above the shoulder to shoulder parallel line. That is the why he must get the elbow up. Once he gets the concept, you can try these drills:
Field Goal hallway - Stand offset from your QB on the back end zone line - roughly 5-10 yards each outside the field goal uprights. Stand so that the uprights between you form about a 3 foot "hallway." Throw the football over the crossbar and through the goalpost to each other. As you get more confident close the angle down to 18" - the width of a receiver and increase the distance between you. This will force a higher release position of the elbow, patience with the wrist, and extension out to the target. If he has "drift" or a slash in his motion the ball will pull off the target line and outside the uprights.
Fooball Foul Shot - Another good drill is to have him stand on the foul line of a basketball court and shoot baskets with the football - the hallway is the 12" rim. Have him square his body facing the basket just like shooting the foul shot and put his elbow- prepass -in the "lead position" at 45 degrees out in front of and above the throw shoulder. Drop the ball comfortably behind the shoulder, just behind the ear(the last position he will be in before any release begins) and have him just fire the triceps muscle only to extend the ball up and out into the basket - have him relax his body - this is all arm. He will have to learn to roll the wrist properly, because the rule is that he cannot hit the backboard, the ball must drop into the basket without hitting the board. This forces extension and control - touch. It slows him down and trains the fine motor skill of rotating the wrist at the proper time with the elbow where it should be. Sorry so long, hope this helps, I just really love this stuff.

Another thing you might check is where he is carrying the ball. Does he get it to a good loaded up position while in his drop? If he is carrying the ball low (below the shelf or line across upper chest), he will have a harder time getting the ball in a loaded postion to make an efficient, overhand delivery.

Coach,
One thing I have done in your situation is have your Q stand stationary with his left foot forward assuming he is a right handed passer, have his passing arm extended straight up in the air and release the ball from that position. Have a coach, back up Q or Receiver stand 10 yards from the Q to catch the ball. I do this with side arm passers and those passers we always seem to get every year that think a football is a shock put. This helps with muscle memory in teaching high release points.
Another drill I picked up from Larry Beckish is to once again have your Q stand stationary with his passing arm bent at the elbow so the ball is "scratching" the Q's back and releasing from that position. This would be done with out shoulder pads. Hope this helps and good luck.

I like the suggestions for in-water throwing, throwing over the cross bar, high arm and the basket shooting drills. You might also try what is called SEATED AND KNEEL DRILL (Spine erect, shoulders parallel)
1. Sit spread-legged on grass, ball on ground each time (get used to picking up the ball)
2. Throw to spot
3. Kneel on both knees; Left knee; Right knee

I know there are a lot of coaches who don't like throwing from the kneeling position. But, there are times when it is useful.

Tiger One:

I have the QB pick the ball up off the ground to both: (1) get him used to/reinforce the upward motion of the ball and (2) simulate picking up a dropped snap. In the case of the side-armed passer, he will probably benefit from sitting and throwing because his accuracy will be poor if he throws side-armed. I'm trying to use some natural conditions to "force" the behavior desired.