Prepare pasta as directed on package. Preheat oven to 400 degrees F. Spray baking dish with non-stick cooking spray.
Melt margarine. Add flour slowly and blend well. Add salt and pepper. Pour in milk gradually, stirring constantly. Bring to a boil and cook for 2 minutes. Continue stirring constantly. Reduce heat and cook for 10 minutes while stirring constantly. Add shredded cheddar cheese and simmer an additional 5 minutes. Add macaroni to sauce. Coat well. Pour into baking dish. Cover with bread crumbs, if you choose. Bake 20 minutes until golden brown.