Spread out the six dynamic cards. “We’re looking for forte”. Move your hand over the cards, hovering a few inches above them. As you pause above a card in turn, ask the students to say “Stop” when they think you’re above the correct card.
They may be guessing, but that’s okay. If they say “stop” on an incorrect card say, “almost” and keep moving your hand. A good order to use is: forte, piano, fortissimo, and pianissimo, leaving the two mezzo cards until the last. This helps them get the mezzo cards in the right place on the first try.