Double Chess is very much like regular Chess, except both sides move twice in a row. This encourages each player to increase their vision and planning beyond just one move.
Both sides get to play two moves in a row on their turn. Either two separate pieces move once, or one piece moves twice. If moving two pieces, both moves may be a check. This results in a double check, which is a highly effective tactic! At the start of a turn, if the King is in check, the first move must stop the check, otherwise it's checkmate.
At first students are likely to make each move one at a time. As the game progresses, help them to choose a second move before playing their first move. In particular, look for 2-move combos where the first move threatens the opponent's Queen and the second move takes it. Other common 2-move combos include two captures in a row, or capturing a piece and then defending it.