A wall is the best practice partner a beginner will ever have: it never misses, it never hits it too hard, and it is always available.
The drill
Stand two racket-lengths from the wall. Let the ball bounce once, then hit it into the wall so it comes back to the same place. Count how many you can do without moving your feet.
What to watch for
If the ball keeps going to one side, the racket face is open or closed rather than square. If the ball keeps dying, they are waiting for it rather than moving to it.
How often
Five minutes a day beats an hour on Sunday. Ask them to beat their own record rather than anyone else’s.
When it is not working
Bring it to the next class and show the coach. A wall rally that has gone wrong is the most useful thing a coach can see.