Scales

My son's been working on the G scale 4 octaves for awhile. The purpose of this is to find most comfortable shifting on the higher register. His teacher wants him to find it for himself since everyone's hands are made differently. My observation is that his thumb is not the longest. I would say it's probably average in length for his age. His pinkie is whole another story. It is very short and the finger tip is curving toward his ring finger. (took after his dad)
He usually works on scales and arpeggios in the morning before he leaves for school for about 30 minutes to an hour. This morning was very frustrating for him. He even started to cry a little. I asked him, "What's wrong?" His reply was "I can't do it!!" I thought it sounded good. So I asked him "What part of sclaes you didn't like about?" He said it wasn't clean. I kinda chuckled inside. 'OK, he is noticing without being told. This is a good sign.' I assured him he would get it. It just takes time.
I think when he trys to shif to the highest position, his thumb position is not stable yet. Usually, people place their thumbs right under the fingerboard by where the body and the neck meets, but if he places his thumb there, he can't reach his pinkie to the note he is aiming, so he places his thumb on the side of the body about an inch below from the neck of violin. It takes longer to get there. I believe that's why the higher register notes get unstable. I don't play violin so I need to let him figure out himself. Even if I could play, my fingers are different from his, so what would work for me probably won't work for him. I am hoping he will come out of this tunnel soon. It just made me feel proud that he is becoming more independent in his journey with his violin study :)