Scoring: Use cones, ball tubes, or a rope to mark a line that runs across the singles court, parallel to and eight feet inside of the baseline. Any lob that lands in the rectangle formed by the new line, the baseline, and the singles sidelines scores one point. For a shot to be considered a lob, it must reach a height of at least 12 feet (the top of the typical tennis fence).
Group: Have the players line up behind the center mark. Feed to alternating corners, making each feed bounce so that it can be hit from three feet behind the baseline at a comfortable height. Each player will run to the corner, hit one ball, see how it lands, announce her total score if it has changed, and then move to the back of the line. If you have an even number of players, switch directions halfway through the drill so that the players hitting forehands will hit backhands and vice-versa.
Individual: Feed a set number of balls and see how many the player can lob successfully. Keep long-term track of the player's best performance out of, say 40. If the player is less skilled at lobbing, you can feed all to one side, but have her recover back to the center after each hit.
Difficulties: The only tricky part of this drill might be getting accurate judgments from the players about whether their own lobs land in. Turning to look at every lob will wear you out quickly, but if you look only when you can tell it will be close, you might find it tolerable. The best solution is to lay out sheets of cardboard or some other material that will make a distinctive noise when hit, if you have enough such material.
