I was working a Jr High game yesterday when the following situation arose.

A is leading by 24 points with about 23 seconds remaining in the first half. Team A is out of timeouts. They tell me they are taking a knee and they do. Both teams begin to leave the field before the clock expires. Team A then rushes back to the line with team B still leaving the field and Team A is seeking to get a cheap score by running another play. I hadn't blown the ready for play and there were about 12 seconds left. I chose to NOT blow the ready for play and I let time expire for the first half by standing over the ball with the clock running. (B was totally confused and they would have never gotten the proper players on the field and they were also out of timeouts).

At the various levels, I am curious as to how you all would handle this. I know college rules support preventing this tactic. Would you do this at a high school varsity game?

Yup. No cheap scores by cheating on my field.

Put the U over the ball, and unless B was there, delay the RFP.
Personally, I'd whack the coach with a UC foul.

Canadian Ruling
 

10 yards misleading tactics.

I'd also see if I could hit the coach with a 10 yard Objectionable Conduct flag.

He'll loose 20 yards in the 2nd half.

He's a Richard Cranium for that move.

If they did manage to get the play off for whatever reason, I might just loose all concentration and blow an IW.

At no level will I let a team get away with this.

NCAA, rule changes in the last 2 years would take care of it.

NF, my mind is escaping me on the rule so help me out. What rule states that A cannot use verbage or movements which indicate to team B that a snap is not immenent.

You could also go with 9-9-3 which states cannot make a "travesty of the game."