I would assume it would be a driver who holds a CDL. You can't drive with passengers on the bus other than the person training you.
Correct. With a permit, at least in my area, you can only drive with a CDL driver, with the same endorsements you are going for. The person must have an S endorsement, P endorsement, or whatever endorsement your state requires, along with the proper classed CDL.
In my state in order to get your school bus endorsement on your license you have to turn in a green and yellow card to DMV. The green card is given by the school district after you get a physical and drug test. The yellow card is given when you have 2 hours watching a trainer drive w/ students, 2 hours driving w/ trainer no students, 2 hours of driving with trainer and students. The way it works is when you get your permit you have to present your green card and pass the school bus test and the 12 hours of in class training. Then when you meet the requirements for the yellow card you present DMV with that and you get your CDL after passing their driving test. So yes you can drive with students on a permit in supervision of a certified school bus trainer (forgot to mention it can't just be a CDL driver it has to be a trainer). I live in DE.