Okay, since we are doing true confessions...
I think I was in First or Second grade (making me perhaps 6 or 7 at the time), and during recess we sometimes played tetherball on the playground:
Well, this one day it was my turn to climb the pole and attach the tether with the ball to the top of the pole. As I climbed, I slipped a few times, and so I grasped the pole even harder with my loins, and thrust upwards.
By the time I got the ball attached, I experienced a euphoric ejaculation, although I had absolutely no idea what had just happened.
Well, to say the least I volunteered to put up the tetherball during the rest of my early grade school tetherball career, LOL.
I didn't actually consciously jerk off until several years later.
True story!
ADG