This document reports the results of two studies performed to determine the effectiveness of special lessons in facilitating the attainment by children of the basic concept "tree." The first study, which utilized 103 fifth-grade students, also investigated the effects of pretesting. Results showed no significant effects of pretesting and no significant treatment effects. The second study utilized 64 third-grade students divided into a control group and an experimental group. Results showed the experimental group performed better than the control group on tests for the formal level attainment of the basic concept presented. (SL)