Coaches being on the field is a very common thing at the middle school level.
I've seen it much more during 7th grade games. They often help players get into position before the play and get to where the kids can hear them. I've also seen this at plenty of 8th grade games.
As for if UIL has any rules about coaches on the field I really don't know.
@B12Fan:
If a middle school aged player needs a coach to line them up - most likely they shouldn't even be on the field. That stops at about age 6.
There are UIL rules about not being allowed on the field except during a called time out. There is a box marked on the field at each sideline that coaches and sideline players are to stay within.
In last nights game the Humble coaches charged out onto the field challenging calls, shifting their defensive players and we're never warned or flagged for it. Totally out of line. Refs did not manage the clock or coach behavior and missed at least a half dozen offsides including easy to spot "lined up in the neutral zone" players.
@lynnsgirl - I was the lady exchanging retorts with the Humble coach at halftime about his whining suggesting he be the role model his players need. His response "I always do this. ever body know dat".
Piece of work.