Epic Fail!

Where do I draw the line? I understand that my students at the Guatemalan school haven't had as much education. I get that there philosophy of learning is different. But this is ridiculous. I just graded their first music exam of the year. In the 8th grade class the majority failed, we're talking 50s - and they admittedly did not study. In the 9th grade class things were brighter. Some students even scored higher than 100, and then there was the 47 and the 28. Yes, 28 out of 100. Argh! I have decided I will give a makeup test during recess next week. It will be much harder, and the highest grade they can get is a 90. There, I guess I drew the line.