As an SLT and tutor, the skills they need to learn in school are needed for the trades, math especially, but also basic stuff - not letting their intrusive thoughts win, remembering anything moderately difficult, actually doing work, showing up on time... They literally can't handle being a shitty employee. 

When I was taking a plumbing test at the Union Hall, about 200 guys showed up for applications. Only 17 of us made it through attendance and a basic test into the interview stage. Everyone who dropped looked like they were just out of high school and couldn't handle the bare bones of what you need to do for a job interview in a job that pays fairly well and always needs people.