This is true for the most part, right now, but an aspect that has been neglected is the importance of getting the right focus and creativity for the others. Almost every child in the "slower" class can do much, much better than he is doing--with the right teaching.
I went to junior high and high school on the campus of a teachers' college, and that thinking was at the root of much of the education of the future teachers.
Teaching kids to love learning is a delicate endeavor. You can't just mouth it. You have to construct things so the kids will simply be engaged with what is happening in the classroom without having to have that concept put into words.