I have never fully accepted the hypothesis that inclusion is "best." Certainly, it is for some students - but not for everyone. And I don't buy the assumption that severity of disability necessarily determines the ability to include successfully; some severely disabled students can be successfully included, while some less severely disabled cannot. I think it depends more on the nature of the disability, the manifestation, and how the student feels in the mainstream environment.
For some students, private placement afforded them the first opportunity to feel safe, and to feel like they were in a true peer group. For others, it was the first time they felt like they had teachers who understood how to teach them. Many students feel "normal" for the first time when they are in private placement. When a student's energies can go toward learning, making friends, and experiencing school the way we expect typical students to do, isn't that a benefit that we want for ALL our children? If our children can do that by being in schools that are designed and equipped to provide that experience for them, and to teach them how to advocate for themselves so that they are able to "face the world" when they move on to their next stage in life, isn't that what we ultimately want for them?
If we were discussing anything besides education, there would be no discussion: if you needed a lawyer, you would look for a specialist; if you needed medical attention, you would look for a specialist. Why is it considered "wrong" for parents to want the educators of our children with special needs to be specialists in the particular needs of our children? Why is it wrong for us to want EVERY TEACHER our child deals with to understand our child's educational needs? We don't want just the "autistic specialist" to know what to do; We don't want just the "SED specialist" to know how not to say things that could trigger a crisis in a fragile child.
I am tired of being asked why a certain support can't be provided to a child within a mainstream classroom - the particular support may be able to be provided, but the kind of environment a child needs cannot be magically provided. Inclusion is a wonderful concept - as a concept. It works for many children, with many diagnoses. It does NOT work for everyone, and it should not be expected to. The current push to do so is completely ignoring the individual needs of the "I" in IEP, for the sake of educational theory/philosophy. It is at a horrible cost for those who are being sacrificed on the alter of philosophical rigidity.