Opportunity to respond has been defined as at least a two-part interaction between (a) the arrangement of antecedent instructional stimuli and (b) student responses to those stimuli. Instructional stimuli are presented in the form of materials, verbal questions, prompts, cues, or directives, and students' responses to those stimuli may be written, oral, or in the form of other motor behavior. The first step of a traditional interaction sequence might be exemplified by a teacher orally asking, “Who was the first president of the United States?” The desired student response would be the student answering orally, “George Washington.” However, the first part of the opportunity to respond also might be presented by a desktop computer program flashing the question, “What is 2 + 2?” to ...