Backboard slap - BI?

Tangentially I had a game tonight where we knew we would have above the rim play. My R asked if we had anything to add so I said, "just want to make sure we agree on the high school rule....the ball can be blocked as long as it is still going up, even if it hits the backboard first".

Both guys looked at me like I was dumb and said no the rule does not say that. As the young guy I didn't argue and kept my mouth shut. So much for knowing the rules!