TS
I'm no good at Excel or math. I'd suggest flunking them all. You'll get a reputation of being a tough teacher.
Make a spreadsheet set up with test dates as rows, student grades as columns.
Use data sort to sort all of the students scores top to bottom for each student. That way all of the lowest scores will be at one end of the column.
Sum the cells containing the lowest grades by student and apply your grade calculation formula.
I was always taught that life is not fair.
If you decide to be fair, you can use the sumif statement; sum all grades >= median.
Are you considering how this will affect their self-esteem?
:-)
Sum them all and then subtract from that the lowest 2 using the SMALL function. A1:F1 is the range of the scores and -SMALL(A1:F1,1) subtracts the smallest and -SMALL(A1:F1,2) subtracts the next smallest.
=SUM(A1:F1)-SMALL(A1:F1,1)-SMALL(A1:F1,2)