A hindered-settling fluid classifier is adapted for processing aggregate entrained in a flowing slurry. The classifier includes a classifier tank defined by walls, and having an inlet at its upstream end and an outlet at its downstream end. A slurry feed pipe is connected to the tank inlet for introducing the aggregate slurry into the classifier tank for processing. A plurality of laterally-extending flow control doors are spaced apart along a length of the classifier tank, and are adapted for interrupting flow of the aggregate slurry downstream from the tank inlet to the tank outlet. The doors define respective material settling zones each located a progressively greater distance downstream from the tank inlet. At least one water line is provided for generating an upwardly rising current in each of the material settling zones to control the settling velocity of aggregate floating downwardly towards a base of the classifier tank. A plurality of collection hoppers are located at the base of the classifier tank and below respective settling zones for collecting and classifying aggregate settling within the zones.