Make an appointment. Ask ahead of time when you should come in — and then stick with whatever commitment you make. If you must cancel, give as much notice as possible.
Wait to be introduced. When you arrive in the classroom, allow the teacher to present you to the group before you jump in. Preschoolers are creatures of habit, and transitions can be tough. So let the teacher manage them at his own pace.
Be fair. Treat all students equally – no playing favorites with your child or his special buddies.
Follow school policies. You may need to register with the director or even get a background check before you can spend time in the classroom.
Look for a role that suits you. While you shouldn't turn up your nose at the mundane tasks that keep a classroom running, you can and should work with the teacher to find volunteer jobs that are a good match with your skills, personality, and schedule.
Stay connected. Keep an active, open, friendly line of communication with the teacher, both when you're volunteering and in other interactions such as at drop-off and pick-up time.
Share yourself. Offer to teach the children about your job, a special hobby, or parts of your culture to bring something new and valuable into the classroom.
Defer to teachers. It's important not to second-guess the teacher's decisions, make changes to projects or instructions, or hang around once you're no longer needed.