Hi Jim,
I am glad that you have success with the pairing approach. The problem you present is a common one. My most successful approach is to first talk with the strong team member and outline specifically what it is that I want him/her to focus on in working with the other team member. Sometimes, the strong team member gets out ahead of their knowledge base, just as you mentioned. Through my talk with them I encourage them to focus on one item that I want them to work on with their team member.
If I have a strong team member that doesn't listen I reassign teams. As a general practice I do this anyway so that I can measure individual growth and just not team growth. It keeps the teams from becoming to dependent on each other. In addition, they learn to work with different personality types, and dedication levels. Strong team members may find themselves teamed with other strong team members and this forces them to negotiate some form of work plan if they are going to complete their work.
Hope this is of some help to you as you create your teams.
Gary