Is there a number of disabled students (as a percent), who when added to a classroom, will negatively impact the overall achievement of the classroom as a whole?

Achievement of the classroom as a whole is more about the students who distract in the class that matter than the number of disabled students in the class. Specifically, more than four to five of these “distracting students” in a class preoccupies the teacher’s attention away from the learning – but then it comes back to teacher expertise in classroom management, making the work not too hard but not too boring, and their belief that their role is to evaluate their impact on the students” (John Hattie, personal communication, September 22, 2016).