Abstract: A plastic buck which is used to form an opening in a wall to be constructed of concrete or other flowable building material. The buck includes flanges on each side which contain mounting holes used to mount the buck to a wall form. Additionally, the flanges include holes for mounting fasteners onto the window buck thereby enabling the fastener to be cast within the concrete wall. The buck includes bracing members configured within the buck to prevent the forces of the building material on the window buck from causing unacceptable deformations in the buck as the wall is poured. Handles are also attached to the window buck to facilitate installation and removal of the buck. A plurality of knock blocks are located on the buck such that one may apply impact forces to the buck to remove the buck from the concrete wall after the concrete has set. Since the buck is constructed of plastic or other nonporous material, removal of the buck from the poured wall is facilitated.