It took 8 months to teach one student how to perform his job functions at a local chain restaurant - selecting a knife, a large fork, a salad fork and a spoon and then rolling them into a cloth napkin. But at the end of that 8 months, he knew how to do his job with perfection and worked there for almost 10 years instead of spending his days in a group home or a bedroom in his parent's home. His IQ was around 65. Other students were taught to peel and core apples at a bakery, detail cars at an auto dealer, and bag groceries at a grocery store. I taught them how to ride the bus, clock in and out, and manage specific behaviors that were a problem in the work place.
I doubt that public school teachers can better prepare low-IQ youths for these jobs than the employers can themselves. Subsidizing apprenticeships would likely be more effective than spending ever-greater amounts on special education.
Do you seriously know an employer that would be willing to pay any amount at all to spend 8 months teaching someone how to do what is only a very small part of a "normal" job description? The only way these kids were taken in by these employers is because there were tax subsidies for being a part of the transitional program. This is such a better use of tax dollars than the money that used to go into supporting institutions that locked these kids away for life.
Where your idea works great is with kids at the opposite end of the spectrum. Our high school offers gifted kids an opportunity to explore mentorships with local employers in a field of interest. Not only does it give the kids some real-world experience, it supplements what can often be a fairly unchallenging academic program at school.
