It looks like NJ's carseat law specifically excludes school buses. I'm not an expert in this area, but since there are no other responses here, I would point out that school buses are a very safe form of transportation, with a safety record that is much better than cars. NJ is one of a small number of states that also require seatbelts on school buses. That being said, school buses' "compartmentalization" safety design is primarily intended for kids over about 40 pounds. You would have to see how well the seatbelt fits, too. If you're not comfortable with the situation then a 5-point harnessed carseat might be preferable. There are some special considerations when installing a carseat on a school bus because the seatbelts can be different, there are generally no top tethers, and the presence of the carseat can affect compartmentalization for other occupants.