A UK teachers group reports that "gay" is now the #1 most frequently used abusive insult at schools.
No doubt the words would be slightly different in American schools, but here are the words teachers report are being used abusively in UK schools (number indicates percentage of teachers who reported that word as a term of abuse).
Gay (83%)
Bitch (59%)
Slag (45%)
Poof (29%)
Batty boy (29%)
Slut (26%)
Queer (26%)
Lezzie (24.8%)
Homo (22%)
Faggot (11%)
Sissy (5%)