This issue is the focus of much research. Theoretically, having an extra assistant in the classroom and having access to special education support services should increase a regular educator's ability to reach all children. Researchers have also found that having children with disabilities in the regular classroom helps all students develop more mature senses of fairness and social justice. There is always the chance that in classrooms where the teachers do not receive adequate support and preparation that negative outcomes could occur. This will depend on the abilities of the regular educator, the extent that this person can work well with the special education support teacher, and the support services negotiated during the M-Team meeting.
Good teaching is good teaching and bad teaching is bad teaching.
Part of the reason for the inclusion movement is a body of research that indicates fairly equal achievement irrespective of whether a child is placed in special education or remains in regular education. According to the IDEA, support services should be equivalent whatever the placement. This is a definite myth. It may be that adults are displacing their own biases about persons with disabilities onto students. Children are amazingly acceptant and tolerant of differences in people.