In Pensylvania, there are requirements for the number of apprentices allowed based on the number of journymen for a state approved apprenticeship. As this is a state requirement it is likely to differ from state to state. Here the state sets cretain minimums, like a tool & die apprenticeship is a minimum of 8,000 hours shop time and a certain number [I forget how many] at night school or an approved corospondence course, passing grades required. An employer can require more if they desire. The state has agents who visit a company offering an apprenticeship to verify that sufficient experience will be gained for approval.