Place your dark chocolate chips in a microwave-safe bowl and microwave for 30 seconds. Stir well, and then continue to microwave at 20-second intervals, stirring between each round in the microwave, until chocolate is completely melted. While it is microwaving, place your milk chocolate and white chocolate chips into separate microwave safe bowls.
Spread roughly ½ of the chocolate mixture over the wax paper in a thin, even layer (it does not need to spread all the way to the edges of the cookie sheet).
Press your broken graham cracker pieces randomly into the chocolate and then evenly sprinkle marshmallows over the chocolate.
Drizzle your remaining dark chocolate evenly over the marshmallows and graham crackers and use a spoon to spread it until all of the crackers and marshmallows are covered (the marshmallows tend to roll around a bit, this is fine, so long as they are mostly covered.
Moving quickly, heat your milk and white chocolate chips in their separate bowls at 15 second intervals (stirring between) until completely melted.
Drizzle milk and then white chocolate over the dark chocolate and then drag a toothpick over the chocolate for decoration.
Allow chocolate to harden before breaking or cutting and eating (it will harden much faster and be easier to cut/break if you place it in the refrigerator).
For a more authentic s'mores taste, you can substitute the dark chocolate for milk chocolate.