RB34:
8-10: I would use mb tempo or games for this group. When they are able to complete 800-1000m of tempo move to next phase. Like I mention earlier speed work would be games/relays/sprint drills etc until they are strong enough to maintain positions.
12-15: Goal would be 1200-1500m of tempo then move to next block. I would use 40-80m runs for tempo. You can start with short sprints 10-20m for 100-200tv if they are strong enough to maintain position.
16: Goal would be 1600-2200m of tempo then move to next block. Tempo runs of 60-100m. Short sprints 10-30m for 100-250tv.
General guidelines…
RB34 I wonder if you could email me directly at higradeco@yahoo.com , need some more of your good advise. Tried sending your a PM but your inbox is full.