Jai is correct. Margarine is one step away from being a plastic. Other factors that contribute to variances in baking results:
type of flour, humidity, altitude, oven temperature, bake ware (aluminum, non-stick (light versus dark), ceramic coated surface, etc), location of racks, and time of day are just a few.
Also, cooking time and cooling time on the tray and off the tray will affect the texture of the cookie.