I don't think it should be entirely blamed on "deaf" teachers. It should be blamed on the form of communication and materials being taught. If the teacher uses ASL, then the students are not going to develop their grammar and language properly than a student would if he or she was to use SEE. As for the materials being taught, teachers often look at deaf students as being "special" so they add more flexibility and reduce the amount of materials being taught. When I was in 6th grade, my teacher taught us idioms. Pretty much everyone who had that teacher could understand what "it's raining cats and dogs" and "work your fingers to the bone" meant. For my high school, those who graduated at the right grade level as everyone else... spent their years communicating with SEE. Those who didn't graduate at grade level, spent their years communicating with ASL.