A screen assembly for grading and dewatering sand includes a frame upon which is mounted a deck having a plurality of apertures therein. The frame is mounted on a base and includes a vibration generating device for imparting vibration to the deck. The deck has a first portion inclined downwardly from a first end to second end for grading sand thereon, and a second portion for dewatering sand thereon. The first deck portion is inclined downwardly at a first angle, and the second portion is arranged substantially horizontally or inclined upwardly at a second angle. Sand may be delivered onto the deck at or adjacent the first end of the first portion, so that undersized particles of sand passing through the apertures in the first portion of the deck as oversized particles pass onto the second portion of the deck, whereby the oversized particles are dewatered.