School kids who ride in packs led by adults to school improve both their health and their grades, reduce traffic and pollution around schools and help cut climate-warming emissions.By Tina DeinesOn a recent autumn morning in Tempe, Arizona, dozens of kids made their way to class on an unusual “bus.” Rather than the traditional yellow, diesel-run whale of a vehicle, this one consisted of children and parents mostly on bicycles, along with a few scooters and roller-skates.