I use this drill to teach players the 1-2-2 forecheck, with the added bonus of also teaching defensemen to use each other as breakout options.
Whether I'm coaching squirts or college players I find the hardest thing for players to grasp is letting F1 continue to pressure the puck as F1, while F3 stays disciplined by becoming F2, sealing the wall and not diving in too low, when the puck switches sides in the O zone, especially when the opponents switch sides via the back of the net.
This 3 on 2 small area game has a great progression into a 5 on 3 game.