This might be of interest to you. You are a private school, so it may not apply directly, but I'd guess it's all part of the same general set of commonly accepted best practices. Private school parent organizations are frequently considered more of a committee, and thus part of the school, than an independent entity.
Alabama Department of Education issues financial accountability guidelines for booster clubs, other school-related organizations
http://blog.al.com/bn/2007/12/guidelines.pdf
Note - the sentence about PTAs and PTOs both having national organizations is incorrect. PTAs do, PTOs do not.
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