Dr. Root showed a position from Fischer-Sherwin (U.S. Championship, 1957), which was reprinted in the December 2011 Chess Life on page 43. She explained (and demonstrated) definitions of double check and discovered check. Then students had a choice of whether to solve the Fischer-Sherwin position or four easier discovered checkmate and double checkmate puzzles from her forthcoming book Thinking with Chess: Teaching Children Ages 5-14.
Two students of the 12 chose the easier puzzles. The rest worked on the Fischer combination, with everyone getting at least the first move right.