I think most of us who teach writing might agree that spell and grammar check may be as much hinderance as help for our students. But as the study of undergraduates discussed in this associated press piece reports (Nando Times and the newsobserver), it may be worse than we imagine:

Without grammar or spelling software, students with higher SAT verbal scores made, on average, five errors, compared with 12.3 errors for students with lower scores.

Using the software, students with higher verbal scores reading the same page made, on average, 16 errors, compared with 17 errors for students with lower scores.