Does your group have a "conflict of interest policy"?  A conflict of interest policy doesn't necessarily prohibit transactions/activities.  It is supposed to ensure that all pertinent information - including any conflict of interest - is presented and considered when making the decisions.  Your group should decide if being president of the PTO and the school board is a conflict of interest.  Even if you don't have a policy in place, it would still make sense to have the discussion at an upcoming meeting.
         - bblake
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