The purpose of this study was to compare the efficiency, effectiveness, maintenance effects and social validity of two instructional methods, Direct Instruction and Simultaneous Prompting Procedure, on teaching concepts (long, old, few and thick) using a parallel treatments design. All sessions were conducted at a private special education center in a one to one teaching arrangement. Results showed that (a) both direct instruction and simultaneous prompting procedures were effective on three of four participants, while direct instruction was effective on one of participants, (b) simultaneous prompting procedure was found more efficient than direct instruction procedure in terms of the number of trials and incorrect responses, (c) participants maintained concepts at the first, third and the fifth weeks following the intervention, and (d) social validity data supported results of the study. Limitations and future implications for research and practice were also discussed.