Our youngest daughter is a senior this year at Denver Lutheran and I know what you mean about earning to much but not enough. We won't take her out as it is her last year but it is really expense and we don't always have the money. With that being said some of our older kids went to public school and I don't think the education was as good.
Would his dad consider helping on this at least until he graduates? It wouldn't hurt to ask! I would talk to the school and maybe they could work something out. (My sister-in-law did janitor work at the school to keep her son in school) Maybe you could free lance accounting or even offer to help with the schools accounting for reduced tution.
Good Luck,
C. B