This is an interesting situation to consider and I see why you are ambivalent.
A few experiences come to my mind. In college, a professor asked me to help tutor some other students and I agreed, since I had plenty of time on my hands. As the semester continued, the complexity of my work load increased and the other students also became more and more in need of help. I ended up feeling burnt out and resentful towards the people I had agreed to help (a lose-lose situation.)
My DH was in this same boat many times in his early career. In a new job, he would quickly gain mastery, become technical group lead, and then feel frustrated that all his time was being sucked away to deal with other people's issues. Also, he noticed that many people stopped trying to solve their own problems because it was easier just to ask him to figure it out. Long story short, he finally found a team of people that cooperate and help each other, but nobody has to carry anybody else's weight. Everyone is equally as talented, so help is reciprocal.
Hmm, just thinking about your desire to teach the value of charity and community... I guess my experience is telling me that those are two different things: investing in community is win-win, but giving charitably has the potential to be win-lose. So I would probably err on the side of setting boundaries for helping others. At least at first, because scope creep is real.
You know, maybe putting together an after school study group could help or you could get the other parents on the same page in a group email. Or something... Anything that helps, but doesn't put too much pressure just on your child.