CDL School after licence?

Do you mean the medical certificate?
Nope, need to have a medical certificate before you can have a cdl. It's a requirement for carrying a cdl and your cdl will be automatically be downgraded to a standard class c pretty quickly if you let your medical certificate expire.

 

Some cdl schools have night or weekend classes that are designed for people that can't quit their day job.
Some trucking company cdl schools pay the students a salary or hourly pay while attending the trucking company in-house cdl school.
Where is your location?

 

If you can pass all the tests to get you CDL without school then do so. Then go to work for a small local company, farm, or do seasonal driving to get your experience. Then you can move onto a better company that requires experience.

Ive never been to any school or official training pertaining to my CDL. And no I didn't get my CDL decades ago either, I got it in 2013. And I've been driving with an OTR company for 3 years now. Before that I wasnt interested in driving full time, but I did jobs that having my CDL could get me better pay and opportunities. Even before I had my CDL I had some driving jobs though... All told ive been in and out of trucks for over 20 years.