At a prior digital analytics company we ran a 3 month training academy where the candidates spent half their time learning our methodology/trade and the other half of the time working on client projects under close supervision. After several iterations of this process we were able to develop talent efficiently. We were able to have our pick of the talent pool to hire as well as source other top performing candidates to other companies in need of the skillset we taught them.

They still allow you to judge the capability of those working on them. And in the US at least, you're not supposed to have interns working on something you'd otherwise have a regular, full time employee on. The whole keeping companies from replacing employees with cheap interns thing.