In the assessment of the classification process of fine-grained aggregates, the method of evaluation the work effectiveness of the classifier by means of partition curve is rarely applied and this one determines the cut-point particle size and the process accuracy. The paper presents a method of determination the partition curves for the screw classifier operating in aggregate washing plant. There were also presented the partition curves for cyclones and air classifiers, with the way of their interpretation. Partition curves can be calculated for a variety of technological devices, for the wet and dry classification of grained materials. The results allow for a precise assessment of the effectiveness operation for individual device and make it easier a comparison of work effectiveness for various classifiers.