What else can we take away to make our point?

My 14 year old has been grounded from his phone, TV, Playstation, Wii, MP3 for 4 1/2 weeks for not doing his homework. He was supposed to get them back at midterm if he had good grades. I got his midterms and he has an F in Algebra because he failed to turn in 10 homework ignments. We then took him out of basketball, he then got 2 more zeros in another cl so we put him into in school suspension for 3 days. Any suggestions?