It might be a mistake, or computer error. Early this trimester my son's math grade dropped to a 30% (F). I freaked for a second before I noticed that the teacher had entered a homework assignment as a test. My son had gotten a zero on this homework (not pleased to see he didn't do the homework, but as homework is only 15% of the grade one assignment is barely a blip on the grade). But given it was entered as a test (60% of the grade) and there had been no tests yet. Emailed the teacher and he fixed it..
Other possibility is it wasn't handed in on time. Starting late 7th grade my kids teachers started taking NO LATE homework. But I wouldn't expect a teacher to give a zero if a student at least tried.
