well my coach told us this, now a days he is 2 meters tall (6 feet 6 inches) he dunks since the beggining of 9th grade he was 6 feet tall. he wanted to go pro so badly and he jumped rope every day for 30 minutes in summer from 8th to 9th, when he got back to school he dunked and was known in his school for that. so he tells our team to jump rope 30 minutes a day so we can jump higher. jumping rope is easy as hell u just jump while watching tv or anything, i jump rope 10 minutes a day and now i can barely toouch the backboard. i am going to 8th grade too and im 5'7 so just jump rope it well help ur vertical, your explosiveness, footwork and stamina and endurance hope this works bro