Darkness youngsters will keep the birds in full feather for the longer races at the back end of the season, natural you will only get about 3 races out of them before they start falling to bits, as you are just starting off with young birds and trying to build a team for 2011 i would choose the natural way the birds would have been schooled had at least 3 races under their belt, stop them at let them mature for 2011 season with out too much stress
Ken