In all my time in rugby union I’ve never encountered an organised gambling school or gambling culture, one of the obvious reasons being that for decades everybody was amateur and had very little spare cash. Even in the professional era, nobody earns a fortune compared with many other sports.
You read about there being card schools at the back of the bus on old-style Lions tours but I would imagine they were playing for little more than matchsticks or beer vouchers.
Football is a different matter. During my year with Southampton I was surprised how the card schools started up as soon as we pulled out of the car park for an away trip and money was at stake.