You raise a good point. I think Knox is so competitive in the younger age groups due to the school’s massive size — approximately 3,146 students across both campuses — which is around triple that of some CAS counterparts. As for Waverley and Barker, I think the attraction of strong 1st XV XV may draw young potential talents into the school through the junior years. More academic schools like Cranbrook and Aloys may not appeal as much to young rugby prospects. If Cranbrook can start posting better results and even win the competition a few times, I think its junior programs will grow in skill, as boys looking to thrive both academically and in rugby will be drawn to the Brook over rivaling, less academic CAS schools.
I also think Cranbrook’s 16s and opens teams are made up of a large number of scholarship players, which gives strength to their 16As and Opens teams — but the younger age groups still rely on much smaller boys to compete. You can’t really give a Year 7 kid a rugby scholarship, because by the time he reaches Year 12, he could be a completely different player and not as good as originally projected.