Apparatus is provided for withdrawing a stream of relatively static bed material from an operating fluidized bed reactor and gravity feeding it through a conduit to an exterior classifying chamber into which a downward flow of air is introduced. The airflow is turned in the classifier to move in an upward direction countercurrent to the flow of bed material. The velocity of the air is such that coarse bed material passes downwardly through the airflow and accumulates in the classifying chamber, while the fines are entrained in the upwardly moving airflow and both air and fines are introduced into the fluidized bed reactor.