Cant enroll my son to summer class?

Question

is there any alternative a school can offer if my son can't go to summer class?i already made travel arrangements and i cant cancel it coz tickets is gonna be so expensive.he's knew here in US and i didnt know that students will need to repeat the whole year if he failed to attend summer class eventhough he only got 2 failing subjects..this is bullshit.im so distressed.i dont know what to do.can they just give my son piles of homeworks just to make up to that?