A swimmer's starting platform assembly and method includes a cylindrical anchor/post mating system having a keyed angular positioning device. Preferably, a starting platform has a cylindrical support post sized for mating engagement within a cylindrical bore of an anchor. The cylindrical support post has a mating key element configured to mate with an anchor key element when the cylindrical support post is inserted into the cylindrical bore to maintain a fixed angular orientation between the cylindrical support post and the cylindrical bore so that the starting platform is fixed with a desired orientation relative to the anchor.