The Reflux Classifier has an enhanced hydraulic capacity due to the presence of parallel inclined plates, which provide for a larger effective sedimentation area. This paper describes the first detailed study of the continuous steady-state size classification achieved by the device under well-controlled laboratory conditions. Separations of silica were performed at typically 160 μm. Following a series of preliminary size classification experiments, an innovative fluidization arrangement was introduced which resulted in a significant improvement in the separation efficiency to levels higher than previously reported using conventional fluidized bed separators. In turn, remarkably high feed solids loadings were used, with satisfactory separations produced using a feed solids throughput in excess of 5.1 kg/m² s, which appears to be about three times higher than the highest reported throughputs for this separation size.