On January 22, 2020 at 14:58 hrs, Units were dispatched for a vehicle accident with possible entrapment - additional information updated to vehicle vs school bus with vehicle under the bus. On arrival crews found a passenger vehicle rear end collision with a school bus with all students still on the bus and one occupant trapped in the vehicle pinned partially under the bus. Command was established and a quick assessment was conducted of the scene which determined that 13 occupants were on the school bus with 1 being an adult and all denied injury. The occupant of the vehicle was trapped in the vehicle and was determined to be priority 1 Pt and a helicopter was requested for transport. Crews began stabilizing the vehicle and extrication while EMS continued treatment and evaluation. The crews of Medic 289 and M3 were assigned to evaluated and monitor the passenger on the school bus which report possibly 3 minor injuries on the bus. The Medic crews reported that the two pediatrics did not want evaluation or transport and after arrival of the school superintendent the children were relocated to a different school bus for transport under the schools supervision. The Pt was extracted from the vehicle and transferred to M2 for treatment and transport to the landing zone. The Pt was transferred to Aircare 2 for transport to INOVA Fairfax. Command was terminated and Units cleared the scene at 16:10 hrs.