It cost the district thousands in tuition. Do a search and see what the tuition cost is - last year it was about 11k per student charged to their home district. The home district for students is "where they sleep" - PA has had court cases about district residency.
Santorum could have sent his kids to public school in Pennsylvania and they would have spent about the same (probably more). Instead they attended an online charter school.
You think the state and the school district are fully entitled to Santorum's tax dollars but also entitled to refuse to pay for his kids' education in an approved program?
Only a strained and bizarre legalistic take -- or a concerted leftist political campaign -- would deny a state's US Senator the same benefits afforded to his constituents.