Michael Dahl 
Shocks! [PDF ebook] 

A thunderstorm rocks a strange-looking bus on its way to school. With each blast of lightning, the bus ripples with shock waves. With each ripple, a boy sees his bus mates split into vibrating twins, then triplets. The bus soon grows more and more crowded, but the boy is in for an even more shocking surprise. Step aboard the addictively creepy SCHOOL BUS OF HORRORS, where the final destination is never expected.