This situation usually occurs because, even though the child is performing well at some skills (eg forward skating), they have not yet sufficiently mastered other skills (backward skating, stopping, etc). Failure to learn all of the skills at any stage will catch up and cause problems at the next level.  Aside from the motivational factor, one child being faster than the others in the group should not impede learning. Coaches normally work on several badge levels in the same lesson. Coaches review skills from previous stages, refine skills at the present stage, and introduce skills at the next stage.