I was reading a debate on education and signaling and commented:
At least one reason why more businesses don't do apprenticeship style programs is that it's illegal, as are unpaid internships.
Another legal issue is that you can't effectively contract for someone's labor AFTER you've taught them. You can train an employee and they can then leave for your competitor. Without the costs spent on training the employees, your competitor can pay them more than you can, everything else being equal.
The closest you'll see to apprenticeship is in (foreign) soccer and baseball clubs, where teams get a legal ownership interest in the players they develop. Since that tied-up-contract process is legal in those sports, most players are apprenticed to a team. In sports where because of the rules and/or legalities teams can't bind players like that, colleges play a much larger part as "farm" teams.
There's definitely a paper there for someone who wants to do some sports economics...