My 9 year old son lags behind all his close friends in sports and video games. I am having real trouble boosting his self confidence. He is a very bright thinker but when it comes to doing he tends to lag behind, not being fast. So in any social dynamics , he tends to be a follower and lets his friends get away with any kind of behaviour. I need help to make him more assertive and able to stand up for himself.

Check out Maslows Heirarchy of Needs. You know, the 4 basics people...need. He could be lacking in the Esteem department. Mabey honing in on and understanding his unique "nacks" or talents, he could study specialised skills, or a task or tasks that he can master to plant the seed of inner competence/confidence. Mabey in the Security section, he values honesty yet cant seem to find it amongst friends, or some sturcture is lacking at home. Or in the Love section, mabey he does not feel accepted appreciated or like he belongs. Or he needs a real sence of "Family". Taking into account his temperement (Keirsey.com) and his personality type within it (kolbe concept) you can really discover whoo he is.