An article here on FR a while ago mentioned that many doctors are reluctant to tell parents that their children are mildy retarded. Instead they describe them as autistic.
I've actually seen that myself. I worked with a student with a documented IQ of 64 (two separate tests over a 3 year period came up with a near identical score), but the mother refused to have the child have MR services. Instead, she 'doctor-shopped' until she found one that diagnosed the child with autism.
The kid is now in high school and doing poorly because the mother insists that he be in all regular classes, such as algebra, world history, etc and then punishes him when he doesn't do well on tests and/or the class.