Nightward, most modern day league payers would not have that much knowldge of scrums and scrummaging as you think. If they've been playing league since, say Under 7s, in Mini-League (which is for Under 7s through to Under 9s) the rules provide for very few opportunities for scrums (e.g. both teams knock the ball on). Thus they can play a whole season and maybe only pack into 1 or 2 scrums in that whole time. Additionally the scrums have no pushing in them.
Even when they get to Under 10s, which is where Mod League rules apply (from Under 10s to Under 12s), they still rarely get scrums - only difference is they go from 8 players scrums to 10 players scrums (Under 10s and 11) or 12 players scrums (Under 12s).
Thus when they get to Ubnder 13s, when full international rules apply, with the safe play code which is adopted in junior rugby league this means that scrums are depowered, there is no pushing/pulling or screwing allowed, only hookers can strike for the ball.
So by the time they proigress to SG Ball, or Toyota Cup, players have very limited experience with contested scrumagging at all.