I recently gained a new adult cello student. He came back this week for his second lesson complaining of a sore wrist in his bowing arm. A bit of a puzzle!
In the course of the lesson I began to explain again the technique of the right hand in holding the bow and the position of the bow on the string. I explained that he needed to have the bow hair parallel with the floor as he lowered it on to the string.
He gave a sudden exclamation, "Oh, I thought the hair had to be flat against the string!" The "aha!" moment! A simple adjustment to the postion of the hand and away he went, with a far more relaxed (and correct) bow hold.
How vigilant we need to be as teachers, continually monitoring our students technique to make sure they are on the right track!