True this. I don't want to teach a high school graduate (or college grad) what interfaces and abstract classes are.. or basic good design of code. My job depends on making progress, not training.

That said, my org supports up to 4 concurrent interns (typically we have 2-3 at any given point), and they could work for 4 months to 2+ years if they want, 15-40 hours/week -- adjustable for summers, etc... But they need to be at a stage where code review is going over application of theory, not telling them about when to use functions.

We lose a lot of interns after 3-5 months, but if they came in knowing the basics, we usually get something out of it (though the cost-benefit is usually negative). We want to support internships, though, so we keep doing them.