A CDL Certificate

Go to a school that has tractor trailers, learn the right way to drive then take the road test. That is what he should do. Without the money to pay for a private school or state aid for a community college CDL program he can find hundreds of employers that will pay for his school in exchange for working for them for a period of time (usually 1 year).

The actual test for class B vs. class A is not all that different except for having a trailer to inspect and do maneuvers with. Otherwise the skills and road test is exactly the same, so if he can do it in a class B truck he can learn how to pull a trailer and also pass in a class A. Your statement about not knowing about those types of trucks is just than, an excuse.

Either way, class A or B, he will need access to a representative vehicle, meaning one that meets the requirements of needing that class CDL and a licensed driver to accompany him while practicing and taking the test. You (mom) are overthinking this and making it more complicated than it needs to be. He will regret only getting a class B unless he only plans to do dump trucks, mixers, trash trucks and other local type vocational work. If he wants to run the road then a class A makes so many more opportunities available.

Lastly, he can always take the class B skills and road test on a class A permit, he will only be issued a class B CDL, but he does not need to go get another permit, or certificate as you call it. Just make sure he takes a vehicle that has a gross weight rating of at least 26,001 pounds with air brakes (if he passed the air brake knowledge test) to the test site, along with a driver that has at least a class B CDL otherwise he will not be able to test, or he will get a class C CDL which is almost useless.