I am in grade 10, 15 years old and 6'1 3/4". I have big hands and can palm the ball...I could touch rim in grade 8 and getting closer to dunking everyday now..it literally takes no effort to touch rim now but whenever I go for the dunk I get the ball above rim easily but have trouble getting that wrist motion to actually throw the ball in the hoop...and help?
Bodyweight squats are a great way to practice your vertical jump because your squat stance mimics the lowest crouch position of your vertical jump. Incorporate these into your routine twice every week, increasing the number or sets and reps as you improve. After you become comfortable with regular squats, consider adding jump squats to your routine.

The simplest method to measure an athlete's vertical jump is to get the athlete to reach up against a flat wall, with a flat surface under his/her feet (such as a gym floor or concrete) and record the highest point he/she can reach flat-footed (the height of this point from the ground is referred to as "standing reach"); fingertips powdered with chalk can facilitate the determination of points touched on the wall. The athlete then makes an effort to jump up with the goal of touching the highest point on the wall that he or she can reach; the athlete can perform these jumps as many times as needed. The height of the highest point the athlete touches is recorded. The difference between this height and the standing reach is the athlete's vertical jump.