Back to Work Schools: Whence the workers?

When a Back to Work School creates new workforce, what pool do these workers come from? The retired? The disabled? Thin air? Is there any potential harm in running Back to Work Schools (provided you can afford the costs)?

Housewives. There is no long term harm, less social security payments. More income taxes and workers. Although, don't go making a lot of schools. Once the max number of housewives that have returned to the workforce has been reached, I suggest lowering the number to like 5 or less depending on if you're going to keep adding population or not. Same goes with disabled workers and special clinics. Hope this helps.