The discriminative stimulus (S^D) is a specific environmental event or condition (a stimulus) in response to which the teacher would like the child to exhibit a particular behavior. Our desire is that the child begin to discriminate certain stimuli (teacher/parent/peer requests, important environmental events, etc.) from the background noise of everyday life, and ideally to recognize that stimuli as something more important than the background noise.

In the context of instructional programs, the discriminative stimuli to which we desire the child to respond are typically an instruction or request from the teacher or parent. However, it is possible to design discrete trial programs around other stimuli. This is often a slightly more difficult, and may require a bit more creativity on the part of the instructor, but responses to many environmental events other than requests are often very important. For example, a child might need to be taught what to do when he hears a particular school bell. Should he line up? Leave for the bus? Get his lunch out? Or he may need to be taught what to do when he sees his classmates lining up, or when he hears a knock on the door, or when he completes a task, or when he walks into a room. Each of these are various stimuli that one might wish to teach a child to respond to.

Guidelines for Designing and Delivering Discriminative Stimuli

• The child's attention should be obtained before making any type of presentation. This may seem obvious, but is often overlooked, especially in the "heat of the moment" in a busy classroom or at home. Often something as simple as preceding a request or instruction with the child's name is enough to gain his attention. But if the child is engaged in some other task, event, or some self-stimulatory behavior the instructor may either wait until that task or event is completed (or, ideally, in my opinion, the teacher could jump into that activity with the child, following his lead, while maybe working in some practice of appropriate target behaviors; the teacher could then return to the targeted lesson later), or may try to disengage the child from that activity if it is not appropriate or desirable at the time, before an attempt to begin a teaching session.
• Early on in a program, especially, instructions should be simple and clear and should concisely communicate only the most salient information. Of course, as the child progresses, the instructor can make use of more natural and more complex instructions.
• The discriminative stimulus used for a particular lesson should be consistent in the beginning stages (as in the example presented earlier, where Joey was asked consistently, "Show me blue."). As soon as possible, however, a variety of instructions in a variety of settings should be used to encourage flexibility and the generalization of the targeted skill or behavior.
• Repetition of the instruction should be avoided. There will be some discussion on steps to take to avoid this (primarily setting time limits on responses) later in this guide, but essentially, we want to avoid nagging kids as much as possible.

The next section is a look at the response.

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