One round
What one round does for 100 students at the 10th percentile
take part
do not
Each student who takes part
Average of all 100
Drop undone this round
Set how many students a program serves each round and how much each of them gains. When a program serves only some students, the average at each percentile moves only a little in any one round, and the gains have to pile up, round after round.
Caveats
Read with care
Next
Equal chances lift every percentile together. Try who takes part, in the explorer.