I'll boldly tell you that many of the top children in your programs who are excelling musically are doing so in large part based upon the early music experiences they had at home or elsewhere during the formative first two or three years of life, including the last trimester in utero as well. Brain development starts to slow down dramatically after 4 and 5 years old. After that, a child's brain is still fairly malleable, but without building a strong neural foundation early, everything else becomes much more difficult later. Of course, like me, a strong intrinsic motivation factors in strongly as not everyone has the best nature-nurture combination in those early years and yet still thrives in music somehow. Hard work, eh hem, I mean hard play!