i think it means that the effects get lesser and lesser. that is, having a child go to an exceptional kindergarten may show the childs improvements in elementary school, but by the time they are in highschool that child is no different than a child that went to an average kindergarten.

i don't know if that is true.

i believe there are some things that really make a long term difference, however these things are more likely coming from the parents themselves and less from the schools they go to.