Is such differentiated pay the right way to attract science graduates who can make much more in industry, or is it simply going to breed discontent among teachers?

More competitive pay may attract science grads who could make more elsewhere, but I'd argue that it's worthwhile to avoid breeding discontent by giving all teachers that same raise. They certainly deserve it for all the extra hours a teacher puts in grading, preparing lessons, and other "homework." Counting all that, my teacher friends put in more hours in a nine-month school year than I do in a twelve-month sysadmin's year, but they make half the money. Besides, if extra money will improve the applicant pool for science teachers, won't it do the same for english or history teachers too?