Rally Masters is similar to other activities seen here to help players develop consistency. The evolve9 version is set up in an event format with timed round robin rounds playing tiebreaks. They readily admit this can get confusing, keeping track of both the rallies and the tiebreak scores. So I am going to simplify it here and eliminate the tiebreak component. You will need some extra stuff to keep track of rallies and score for this activity, so have some clothes pins and extra balls on hand. Prefer the balls be a different color or type than those being used for play.
Organize players ahead of time into a round robin format. Each round will last 10 minutes. Points may only be scored once a minimum number of rallies is completed. First point requires 2 rallies to be completed. Second point requires 3 rallies. Third point requires 4 rallies, and so on. First ball of each point is bounce fed from baseline.
It is important that there are simple and highly visible scorekeeping methods available, especially for younger players. They must keep track of how many rallies are required as well as what the current score is. Consider using on-court scorekeepers (the flip kind or the tower kind, either are fine). If those are not available, use clothes pins. As for keeping track of how many rallies are needed per point, consider placing balls at the center of the court against the net. That way both players can easily see them, and just add a ball after each point. Ideally you will have different colored balls available for this purpose so that the players don't accidentally pick up and use a ball that should remain at the net for tracking the number of rallies.
Winning players are those who achieve the highest rally of the day.