Mission Possible is a drill from Mike Barrell at evolve9.com. Mike is an industry leader in the field of coaching young tennis players.
Have players play a tiebreak. They are tasked with a challenge, such as keeping the ball deep or hitting to their opponent's backhand. Keep pad and pen handy courtside, and have the players keep track of how they are doing meeting the challenge, or 'mission', in between points. The tiebreaker is played/scored as usual, but the challenge of the mission should be of primary concern to players, second only to winning the point.