Originally Posted by Kayty
When was the last time he has his teeth done and saddle repacked?
If he's a school horse, he's also probably very used to riders with unsteady hands, so the gaping mouth and pulling may very well be him trying to protect his mouth. In this case, you need to have very good, forgiving and quiet hands to let him know that he's not going to get 'gobbed' with you.
He is getting his teeth done in May but I don't think his teeth are an issue either because he's been doing this for a while, even after he has had his teeth done. I do notice that the rider does pull back a lot even when unnecessary but a lot of the time she needs to sometimes keep a tight rein because he has the bad habit of stopping and putting his head down to graze. But we are working on getting him to stop stopping to graze when not given permission to.