Da 1:5b They were to be trained for three years, and after that they were to enter the king's service.
Da 1:17a To these four young men God gave knowledge and understanding of all kinds of literature and learning.
Here is another interesting detail. Daniel and his friends were trained by the Babylonians for 3 years, but it was God that gave them knowledge and understanding. It was as if they were in two classrooms simultaneously, one earthly and one heavenly.
I have found that when listening to the word of God preached, the same can happen. I will receive instruction from the man, but I will often also receive separate revelation from the Holy Spirit at the same time.
What is exciting about this passage is that this was happening not during spiritual instruction, but secular training! Even in our day-to-day work we can receive revelation from God, and not just about spiritual matters, but on how to do our Jobs. God can teach us how do be productive in our workplace better than our employers. God wants us to be shining examples like Daniel and his friends, not just by our behavior and attitude while at work, but by how well we do our jobs too.