this is the rule:
Timing Adjustments—ARTICLE 2
Approved Ruling 3-2-2
I. At halftime the score is 56-0. The coaches and the referee agree that the third and fourth quarters should be shortened to 12 minutes each. The coaches also request that the second half be played with a “running clock,” i.e., that the game clock not be stopped. RULING: The remaining quarters may be shortened to 12 minutes each. However, the “running clock” is not allowed; normal clock rules apply for the entire game.
That being said as long as both coaches agree they just run the clock in high school.