Preheat oven to 350°. Prepare macaroni according to package directions.
Arrange croissant cubes in a jelly-roll pan. Bake at 350° for 6 minutes or until lightly browned.
Grate all cheeses using the large holes of a box grater.
Melt butter in a heavy saucepan over low heat; whisk in flour until smooth. Cook 1 minute, whisking constantly. Gradually whisk in milk; cook over medium heat, whisking constantly, 5 minutes or until mixture is thickened and bubbly. Add cheeses, salt, and pepper; stir until cheeses melt. Stir in macaroni.
Spoon mixture into a lightly greased 13- x 9-inch baking dish. (Dish will be full.) Sprinkle croissant cubes over macaroni. Bake at 350° for 20 minutes or until macaroni is thoroughly heated and croissant cubes are golden brown.