I always reach back to my own experiences in DISD when I write on this. I had one teacher, who taught chemistry. DISD refused to remove her even though only 20% of the students in all her classes were even passing (C- or better).

If you have 80% of the kids on your 5 classes (roughly 150 kids total and 120 of them were failing the class) periods per day who were "not getting it" to the tune of D's and F's, I think that's a pretty clear indicator that you need to find a new line of work.

Worse yet, I don't think this will have the effect DISD is looking for. Teachers with proven track records will likely get offers to move on to greener pastures leaving DISD with the dregs.