The best form combines practicality with a bit of cheerleading and is very careful not to intimidate. Remember, parents are a bit afraid of volunteering (like if they volunteer once, they'll be sucked in to a major commitment), so you need to make it clear that flexible opportunities are available and limited help is still very much appreciated.

While including specific opportunities is great, I also highly recommend including at least one check box that says something like: "I'd love to find some way to help this year, but my schedule is crazy and I'm not sure what can work." You can then reach out to those who check that box and see whether there's something you can work out together.

If you're in volunteer-getting mode, I also recommend this feature story on connecting with more volunteers. Good luck!