A scramble is underway in Ohio over a staple of the back-to-school season: rides on the big yellow school bus. Public school districts canceled bus transportation for thousands of high schoolers again this year while in some cases still busing students to private and charter schools to avoid steep fines under state requirements. A nationwide bus driver shortage is being compounded by the effects of Ohio’s recent expansion to a universal voucher program to help more kids attend private schools. Districts have been required for years to transport voucher students, but disputes over how to do that are intensifying as the program grows.