What was taught to them by in large was taught by Christ and later The Holy Spirit. This included corrections among themselves. Of the ones of higher education Matthew and later Luke by their trade and Paul by his before his conversion. How many lettters did Paul actually write by his own hand BTW? John likely could write toward the end of his life. But fishermen were laborers and it was a very demandiing and dangerous job. If a trade had been there easier for them as more educated I'd say they would have taken it. It doesn't mean they were ignorant or stupid it means they weren't Scribes.
Christ called four fishermen. In modern day He could have called four steel workers on a high rise or four farmers plowing a field with a mule and made preachers of them without college. BTW who taught John The Baptist? The answer is in scripture. John The Baptist was born with knowledge of Jesus Christ. 1 Corinthians ch 1 I think pretty much says it all.
cva66snipe, if you advanced an argument I would take you up on it. You offer only personal opinion based on nothing. If 1 Corinthians 1 pretty much settles it for you, I will leave you to your own wisdom.