MP Mike Wood took a ride on the first yellow school bus in his Batley and Spen constituency.
He joined pupils from Hartshead Moor School on their ride home.
Metro runs 56 yellow buses in West Yorkshire, serving 3,500 pupils from more than 100 schools.
By July the service will have expanded to 90 buses, serving 9,000 children.
Mr Wood said: "These schemes don't just benefit the pupils and reduce traffic on the school run, but they also help the environment and the schools involved.
"Metro has put £18.7m of Government cash to good use by providing this quality service."