You are the parent... Who do you believe?

Option B-Teacher: Claims that student never turned it in. Teacher cross-checked both paper and online gradebooks, looked in late assignment box, looked in "missing from class" box just to make sure it wasn't there. Teacher in process finds an assignment that the student never picked up. Teacher has successfully used this method for the last 4 years. Teacher has not lost a student assignment in 9 years.

Option A -Student: Current assignments missing... 9. Claims he turned in assignments 1&2 way back in February. Claims that the teacher lost the assignment and that it is unfair that they are currently receiving a grade of zero on said assignments