I agree with antisparkle. High school kids are a lot more autonomous than middle school, and elementary school students, and will be more likely to show up the space without their parents. Also, we have quite a few ADULTS that lack the maturity to treat the equipment with care, and clean up after themselves. Not to seem like an out-of-touch old fart, but I doubt minors will treat our space with better care.
Also, there are reasons why car insurance rates on high school students are higher, statistically they are a bigger liability. Not to mention, legally we are responsible for them, and as they aren't members aren't required to sign the liability forms. Also, even if they signed some forms, I'm not sure how legally binding they'd be.
If we proceed, I'd advise establishing strong relationships with the parents of the students we bring in, and have it as a sponsorship program. Also, have both the student, and parent sign liability and responsibility forms to reduce our liability.