A bus company providing contracted a service to a school stated that they separated boys and girls on their school bus in order to comply with health and safety regulations.
HSE Myth Busters Panel opinion:
There is certainly no specific health and safety at work legislation that requires boys and girls to be separated on school buses. But bus operators do need to find practical ways to control rowdy behaviour. This is primarily an issue of good discipline, and pupils moving about a bus or misbehaving can create real dangers for themselves, others on the bus and other road users if the driver is distracted.