Using contingent praise is a proactive strategy for increasing on-task behaviors in special education classrooms. Although there is large body of literature supporting the use of praise to decrease challenging behaviors and increase desirable behaviors, a consensus on how much praise is needed has yet to be reached. In an effort to identify optimum rates of praise, this study used an alternating treatments design to examine the comparative effects of three different rates of praise on the on-task behavior of five students with autism. The results varied across participants, but overall indicated that four or more praise statements per minute resulted in higher percentages of intervals of on-task behavior. An important implication of this study is that teachers of elementary students with autism should aim for praise rates between four and eight per minute, and that a MotivAider® can be an effective tool to help practitioners reach that rate.