What was central to Christ’s means? Mark 3:14 explicitly states it, “with Him.” The priority for the Lord was that the 12 be with Him. They needed to see His life, hear how He interacted with His culture and the people who He encountered and who were drawn to Him. They walked all over Israel and some of the surrounding area for three years with Him. They saw Him interact with all kinds of people, in all kinds of situations. They did not understand a lot, most, of that to which they were exposed. However, later, after Acts 2, it began to sink in.
Note also that Paul followed the same model. He drug a group of men along with him during all of his missionary journeys. Look at 2 Timothy 4:9 – 15, there Paul relates to one whom he dispatched to Ephesus how he had dispatched the rest of the troops….
So, bottom line, the two models we have in scripture have content sure, but that content is given in an ongoing relationship that involves co-laboring in mission. The apprentice sees the master working, ministering, teaching, and also receives explanation beyond what the masses hear. They are then given assignments for which they get feedback.
Sounds a lot like what every professional educational model we have, does it not? Why is it done so infrequently?