Manually preventing a 'happy tapper' from pressing the Home button on an iPad, and getting out of the app you want him/her in, is frustrating. You can engage in Guided Access and 80% of the time that works.

When it doesn't, there's BubCap Pro. A thin, stiff, self-adhesive plate that covers your Home button. It has a hole in it big enough for a pencil/pen point for a teacher/facilitator to get to the Home button.

The adhesive has been shown to prevent learners from prying off the BubCap Pro.