I think this is a misconception, seen over and over again on this board. There are many streams at school - social development, learning to listen, respecting other children, fitting in the routine, etc. The learning part, in the early years and even in year 1-2, almost comes second to the challenge of being able to learn along others. This applies to talented children, children achieving the 'average', and children in the lower sets, and also children with sen. Yes, I can guarantee you that all children will, at some point, be bored at school. Probably most days. There is no reason why a higher achieving child should be constantly challenged or stretched. I think that this would be damaging for them. They all have to learn to learn independently. I have two children, one G&T and one just above average, and the challenge is to try and help them both to be more resilient; accept that they will not win all the time; that they may be told off or may not get the right answer.
My DS who is G&T in maths, science (and very good at music) is not always stretched and challenged at school and I am grateful for that as he has had to learn to entertain himself, use his initiative, make friends, learn to play football, etc.
And also, most children - of all levels - will be able to achieve more at home when they have the full attention of one adult, as they do in a classroom where there are lots of distractions, things to play with (in the early years), and they are one of 30 children.