The problem of preschoolers' intellectual diagnostics is considered. The attempt is made to clarify the role of dialectical mental acts in child's intellectual development. Experimental study of image-bearing form of thinking was performed using L. A. Venger's, N. E. Veraksa's, D. Roeter's, R. Pintner's methods. As many as possible of the peculiarities of 6-years-old children's intellectual development were taken into consideration. Experimental data show that dialectical mental acts comprise independent units of thinking's analysis, so even on the level of image-bearing reflection dialectical thinking plays the role of independent intellectual activity form.