It is graduation day at Stanwich School in Stamford, and 13 students who were aboard a bus that crashed Wednesday missed the event.

Police say some of the students remain hospitalized. News 12 has not yet received word on their conditions.

The bus was headed from one high school in Stamford to another in Greenwich, according to investigators.

Police say they are unsure what caused the 74-year-old school bus driver to crash. They say they are running a safety inspection on the vehicle and a background check on the driver as part of the investigation.