An adjustable keyboard tray has a top and a bottom plate made of a polymeric material that are bonded together, preferably by ultrasonic welding. A cavity exists between the top and the bottom plates wherein a pocket can be formed to receive and secure a bracket for a mousing platform. The top and the bottom plates can also be formed with recessed areas to flush-mount brackets and maintain a generally overall smooth outer surface to the adjustable keyboard tray. A slidable mounting plate secures the adjustable keyboard tray to a bracketing mechanism mounted to a horizontal surface. The slidable mounting plate allows the adjustable keyboard tray to move in a lateral direction substantially perpendicular to the bracketing mechanism for repositioning the adjustable keyboard tray with respect to the horizontal surface.