I work with a 7 year-old boy on /s/ and he is at the carryover stage of therapy. He tends to do well in structured situations but forgets his /s/ in less structured situations like playing a game. Finally I figured out what motivated him–I told him that if he heard an incorrect /s/ in my speech when I was talking, he could get an extra turn, and if I heard the same in his speech while talking during the game, he would lose a turn and I would get an extra turn. Wow, did that motivate him! He started listening to me as well as himself and being more careful in his productions of /s/.