Preheat oven to 350 degrees. Prepare brownie mix according to package directions. Spread into a greased 9"x13" pan.
In a medium bowl, break graham crackers into 1 inch pieces and toss with miniature marshmallows and milk chocolate. Set s'more mixture aside.
Bake brownies for 15 minutes in the preheated oven. Remove and sprinkle the s'more goodies evenly over the top. Bake for an additional 15 to 20 minutes, or until a toothpick inserted in the center comes out clean. Allow brownies to cool before cutting into squares.
These brownies were a big hit at our house! I made them for my son's birthday, then a couple days later made another batch to take to a church dinner. They're so easy since the base is box brownies.