I'm doing my first FMQ in a heart design. Keeping a good, steady speed while feeding the quilt through is a challenge! There are some places where the needle skipped, but I'm taking heart that practice will help me get better. So, I'd say remind your students that, like everything else, they'll improve the more they do it!
Talk about thread tension. Above quilt has a double cotton batt which definitely affected the tension I'm using.