Here are some relatively firm numbers from the Special School District of St. Louis County, Mo. This district was established specifically for special ed, and is open to every special ed student in the county, whether they go to public or private schools, are homeschooled, or are homebound due to medical or other issues. So it’s a pretty comprehensive cross section.
The district serves 24,000 students. That includes two countywide vocational/technical high schools that the district operates. They account for 1,800 students; the total receiving special ed services is actually closer to 22,000.
Out of those 22,000, 97% receive special ed services in their “home” school, alongside “normal” students. About 750 attend schools totally focused on special needs. Some of those kids are so severely physically disabled they need their own attendant and pretty much 24/7 care no matter their intellectual skills. Some of them really should be going to an “alternative” school, but they got slapped with an unspecified category of behavioral disorder, and were diverted into this system. The rest of them are what we would all consider “special ed students.”
Those students need something close to 1-on-1 attention. My wife’s typical “class” size was maybe 7-10 kids, and most years she had a lull-time aide or assistant assigned to her. They were taught different subjects at different times throughout the day (sometimes by a teacher who specialized in something like math, reading, or domestic life skills, but most hours by my wife), so in that sense they were in classes.
According to the state of Missouri, 301 students were in Phase 3 high school programs. Anecdotally, a lot of those students seem to have started out in regular school, but fell farther behind each year until they needed special attention in every class. The 5-year high graduation rate was about 27%-29%.
That means about 1/4 of the students with the most intense intervention did well enough to earn a high school diploma. A lot of my wife’s graduates seem to have ended up in food service or custodial work. The rest of them would either a) drop out before graduation b) learn enough skills to work in a sheltered workshop c) not really have that level of skills, but enough skills to live in a group home with supervision. The rest could be considered a complete failure of the system.
The district’s per pupil cost is $15,146, spread out among the students who need only the most minimal of assistance to those who are totally dependent on special services.
That number is on top of what the participating school districts spend, which ranges from $11,124 to $23,811 per pupil.
TL;DR. Special education is expensive, and can cost twice what a school district would spend on a typical student. Few students need the most intense level of assistance. A little more than 25% of the time, the outcome is good enough to ensure that even those students can at least graduate from high school and find a minimum-wage job. Most of the rest will have learned enough to at least minimally function in society, with a lot of supervision.
Is it worth it? YMMV.