I´v reschooled a few Standis that came off the track, exallent learners and will give their heart and soul if given the chance. The more you work with them the better they get, (can apply to any horse) but I feel Standis can be a little sensitive and need a little time. As long as they understand what you want they will do it if possible.
You can go a loooooong way with a little TLC & Patience.
Oh, it can help to have an old tug boat horse with the first few times you hit the trail, helps to keep em calm and build up the self confidence.
Remember, Standis are movers, so let em take the lead, if he comes to a bawlk turn back to the ol tug boater and hitch a ride behind, once pass the imagined danger they will usely want too take the lead again.