When to get private tuition

How does anyone know when they need to invest in a Private tutor? I have three children and they all learn at different speeds and in different ways, my eldest didn’t have a Private tutor yet he struggled with a few subjects and seemed to pull through it in the end, he just asked a few family members including me for a bit of Tuition in subjects they were particularly good at and it seemed to work.  My middle son didn’t have much trouble and we never even imagined looking in to getting a Private tutor in fact Private tutoring never even came up in conversation! A little extra tuition after school with the existing teacher the odd time seemed to be enough for him to move on. Now we have a different situation with my youngest, he seems to be loosing his confidence and wont accept any tuition from myself or his siblings, he is too embarrassed to ask for help from any other members of the family too. When I was chatting to my sister she told me that she got some Private tuition for her daughter and it worked wonders, I didn’t even know about it and she told me that her daughter had specifically asked her not to tell anyone she was getting private tuition. I suggested to my son that we look in to getting him some Private tuition and at first he was set against it because he didn’t want anyone to know about it.