Dr. Root had all three groups play "the pawn game" which is simply king and 8 pawns versus king and 8 pawns. It is featured in Science, Math, Checkmate: 32 Chess Activities for Inquiry and Problem Solving. When pawns promoted, players tried to use what they know about checkmating to try to checkmate their opponent.
While students were playing the pawn game, I individually taught:
1) beginners how to do the two-rook checkmate vs. a lone king
2) test (and reteach) intermediates the one-queen checkmate vs. a lone king
3) test (and reteach) the one-rook checkmate vs. a lone king to the advanced players.
Before the beginners played the pawn game, Dr. Root reviewed the normal pawns moves, captures, and promotion but did not cover en passant yet.
With the other two groups, Dr. Root reviewed en passant and ask them to raise their hands if it came up in their Pawn Games so that Dr. Root could double check that they were using that rule correctly. Dr. Root also reviewed promotion rules with all three groups.