As a teacher one thing I found frustrating was when the curriculum said to get them to the next belt in 3 months and the attention span was not there.
Some kids need a lot of time.
Honestly the other was the parents' inability to let the teacher teach. They want little johnny or susie to be as good as everyone else, learn as fast as everyone else, pay attention as long as everyone else so they get in there and start yelling at the kid. We had a rule at dojo #1 that the parents could not participate once class started unless invited. The dojo #2 has parent participation in every class all the time.
As long as they get what the program is and help it was great but I cringed when the kid was getting yelled at.