I have rented my condo to international students who trashed the place and got evicted. Can I hold their sponsor (language school) accountable?

What do you mean "sponsor?"  Are you just talking about sponsorship in relation to immigration status or did the school vouch for the student's character and/or creditworthiness to you?  Did the school co-sign or guarantee the lease?  Do you have any sort of agreement with the school regarding leasing space to its students and if so what does it provide?  If you have no contract with the school making it responsible in some way for its students conduct, and if the school did not make any misrepresentations to you about these students, then I don't see what basis you have to hold the school liable for the students' obligations.