James Altucher's blog recently. In it, he talked about the time he interviewed basketball legend Bill Bradley. You don't become a legend without putting in the work, even if you are almost seven feet tall. One of Bradley's challenges he imposed on himself as a practice drill was to make 15 baskets in a row from five different spots on the court. If he missed, he had to start over. I love this idea for improving consistency and stroke technique.
Adapting the concept for a tennis lesson offers endless possibilities.
Challenge your students to hit X balls into play in a row from a given location on the court. You can have them rotate in one ball at a time (hit-n-git) or they can stay in until they miss. First player to meet the challenge, wins.
Add hitting locations after each challenge is met. For example, hit 10 balls in, in a row, from the deuce side service line. Once this is accomplished, move in and hit from return of serve position. Then to baseline position (notice they are progressively more difficult!). Repeat on ad side, etc. If your students are beginners, this could take some time to accomplish, so you can spread it out over a series of sessions, or give them, let's say, the month of March to achieve the goal. Definitely offer recognition or prizes for the winners.
For young red ball players, keep the number of balls required under 10. If hitting consistently is too difficult, substituted catching and throwing to a target instead.