I make my comments based only on the information given above, and as a teacher of writing in both the university and high school setting.
Let’s proceed. Having said that, I question the phrase, “coherent sentences”, and wonder aloud if “cohesive sentences” may have been the appropriate term, or quite likely, “grammatically correct sentences”.
Not being able to write a “coherent sentence” means quite simply, the students were writing incoherent sentences, or put another way, sentences which make no sense. I wonder how true that statement is of the previous situation at New Dorp High School.
Next, we are told that a return to a focus on the fundamentals of grammar and expository essays brought tremendous improvement, described as, “soaring pass rates for the English Regents test and the global-history exam.”
Related: The Writing Revolution by Peg Tyre.