I'd definitely echo this. Coaches are generally supportive and are particularly keen to clamp down on dissent; if I speak to a player re dissent they are generally subbed pretty quickly or, as happened at the weekend, will be taken to one side by the coach at the next break in play.I will say that in my limited experience of academy fixtures, coaches have always been very supportive. If you pull a player aside to give him a public bollocking, you'll almost immediately see the coach send a sub to warm up and that player will have been pulled off to calm down within 5 minutes, even if it would only have been a yellow card-level offence.
I've been fortunate enough that I've only seen one red card offence in an academy match, and that was DOGSO when I was on the line of a competitive U18's match where cards are to be applied as usual. But if I'd been in the middle of a lower age level match and seen a player throw a punch, I'm not continuing the game with him on the pitch - the only concession to it being an academy match is that I will give the coach a brief opportunity to sub him off. If he doesn't want to play the game and refuses to enact the sub, I won't play along any more either and will just send the player off - however again I want to emphasise, nothing in my experience of academy matches so far has suggested this would be at all necessary.
I've been fortunate that until this incident I've never had a red card offence committed in an academy game but to use your example @GraemeS, if a player threw a punch there is no way I would restart the game with that player on the pitch. If that meant showing a red card because a coach refused to take action and no longer getting fixtures, then so be it. I also think it's important to make the distinction between sanctioning by asking for the player to be subbed v. taking no action at all. Having a player removed from the game has exactly the same effect so I can accept it as being part and parcel of younger age academy football (even though I don't like it), but doing nothing is not, and should never be, an option.