I wouldn't worry too much about what spin he is imparting on the ball. Most little league throwers put a gyro spin on the ball. My 13 year old still puts a semi-gyro spin on his fastball. This happens because of two things usually- a low arm slot and good early arm pronation. In the big leagues, natural sinkerball pitchers are also imparting a semi-gyro spin on the ball, thus why it sinks.
The truth of it is, not very many pitchers put a true perfect backspin in relation to the ground on the ball. If they did, their pitches would be perfectly straight as an arrow and that is not a good thing. Backspin is naturally created by the flip of the wrist when a person throws whether they think about it or not.
A sinker ball is achieved in several different ways by different pitchers. A lot of it depends on the pitchers arm slot. The lower the slot, the more the ball will sink and fade due to the spin in relationship to the ground. More over-the-top pitchers have to use different grips to achieve this same result by throwing the ball and imparting less spin across the seams. A Good split finger fastball and even a cutter can be a good "sinkerball" type of pitch.
Don't get confused thinking a gyro type spin is bad on a baseball. If a pitcher can throw his fastball with more of a gyro spin and can throw it with good velocity he is a heavy favorite to be the much sought for sinker ball pitcher. The gyro type of spin is imparted at the very last 100th of a second as the ball leaves the pitchers hand. What happens is that the arm starts to pronate (palm side starts to rotate outwards towards 3rd base for a right hander) right at release point. As the wrist begins its final snap, it is in a more rotational movement due to the early pronation which gives the pitch the gyro spin. From the pitchers view the pitch will gyro in a clockwise direction and opposite from the batters position. The advantage with this pitch is that most of the time the spin will be slightly off center causing the ball to move more in one direction than another but never quite the same. This of coarse can't be noticed until it gets up around 65-70 mph.
Don't worry about the actual spin rotation. Worry more about velocity and arm strength. A lot of times, as kids grow their spin will change naturally as the hands and arms grow and mature. I would say that about 8 out of 10 kids below the age of 11 put a gyro spin on the ball. Don't worry about it.