The Division for Early Childhood of CEC has a position paper on inclusion that includes the following statement:
“Ideally, the principle of natural proportions should guide the design of inclusive early childhood programs. The principle of natural proportions means the inclusion of children with disabilities in proportion to their presence in the general population."
The DEC guidance is a philosophical one. No research studies have systematically compared different proportions. About the only things that can be said from research are that (a) inclusion has resulted in increased social and functional skills for children with disabilities, compared to self-contained programs; (b) it has resulted in more altruism and “acceptance” (hard to measure) by children without disabilities, compared to programs with no children with disabilities; and (c) old studies of early childhood special ed settings that might or might not have included children without disabilities (i.e., reverse mainstream, special-ed-oriented classrooms) were of lower quality than were inclusive settings.
So what are ideal ratios? Philosophically, some people, like DEC, say natural proportions. Programmatically, some people like me prefer a setting where there are enough children with disabilities that all children benefit from the good things that come from early childhood special education (e.g., individualization, specialized information to teachers—from therapists or itinerant ECSE teachers, family-centered practices, effective instruction) and retain the good things that come from early childhood education (e.g., developmentally appropriate practice to promote play, emergent literacy and numeracy, and social-emotional development). This percentage of children with disabilities rarely should exceed 50% or it is in danger of becoming too focused on special ed. The key ingredients in an ideal program, then, are the two sets of examples I’ve just given. There is no ideal ratio.