I have my doubts that what you say is true.
Let me clarify: I don't doubt that special ed costs a lot; I just doubt that such costs are included in the typical "per pupil" costs we see quoted for public school systems.
And on a different note, I also doubt that even 1% of pubic school kids recieve $100,000 worth of individual services each year. And I bet most of the 15% do not really have special educational needs - rather I bet they fall into the do-gooder-ever-expanding-we-need-more-cash-for-my-special-program-its-for-the-children-after-all-and-if-you-ask-me-50%-of -the-kids-should-be-in-the-program-since-that-would-give-me-job-security-and-a-bigger-budget category.
There are very few special education children that cost 100,000 a year, far fewer than 1 %. The higher per student cost is certainly not all because of special ed, but it does make a big difference. When you think of special education you have to consider all types, not just ADD or learning disabilities.
Consider just the equipment costs of making classrooms and bathrooms accessible for students in wheelchairs. Braille books for the blind, captioned media for deaf students. Counselors for mentally ill students. Equipment that helps students with speech impairments speak. Medical equipment for students with severe physical impairments. And on and on.
Private schools have a big economic advantage. Yes, they are probably more efficient. But, comparing cost per student in private schools with public schools is not an apples to apples comparison.
If you want to know the specifics.
From US Dept. of Education (1999-2000)
$50 billion federal, state and local tax dollars spent on special ed.
$ per student in special ed: $12,474
$ per student in general ed: $ 7,556
Federal funding = 7.5 % of special education spending
Cost of referral, evaluation and IEP development (in addition to special education costs) $1,086 per student
From 1977-2000 special ed spending increased by 30%
ration of cost for special ed students compared to regular students decreased from 2.17 to 1.9.
On your point about 15 % needing special ed. Without a doubt the 15% includes many who do not, but they are probably not using much of the resources comparatively. Here is a rough break-out of the 15%.
Specific LD (dyslexia, dysgraphia etc.) - 50 %
Speech & language impairment - 20%
Severe emotional disturbance - 9%
Mental retardation - 11%
Other health impairment - 10% (includes 4.5% ADD and 1% autism)
Gifted and talented does not fall under IDEA and is not included as part of these special ed. numbers.
Yes, public education is inefficient and there is certainly waste and abuse. We want it to be all things for all people, and that is not possible.