A CLP (Commercial Learner Permit) with a P (Passenger) or S (School Bus) endorsement will also carry a P restriction. You are not allowed to carry any passengers in a bus while driving with a CLP. This includes other students in a driving school. Only properly licensed instructors will be allowed in the passenger vehicle while a CLP holder is driving.
A passenger endorsement is required if you are driving a vehicle designed to carry 16 or more passengers, including the driver. The endorsement requirement is based on the maximum occupancy rating of the vehicle and not how many passengers are actually being transported.
If you have a Class A CDL with a P (Passenger) endorsement, you will also have an M restriction. The M restriction prohibits the driver from operating a Class A passenger vehicle, which is a combination tractor with a trailer designed to carry passengers.
School Bus is a separate endorsement and also requires a Passenger endorsement. The School Bus endorsement is only required if you are driving a school bus with a stop arm, carrying children. School Bus is not required for driving activity buses for school districts, though your school district may require it.