My lad had a drill with the county coach we use at the club. He kneeled down on the wicket (where the ball would normally bounce if bowled short) and threw a tennis ball up from ground level. This allows the batsmen to practice the basic response to short balls in a rapid and regular manner. Repetition of practice is a problem with net sessions.

I would start with this drill to check the basic body position and shot. Then I would move to throw-downs, with a proper ball once you're comfortable. I would also consider the use of a hard rubber ball. The right type can get a reasonably authentic bounce at high speed. The real thing will seem easier after!