Assessment of stimuli controlling the requests of students with severe mental retardation during a snack routine.

Three teens with severe intellectual disability had learned to ask for snack items after a 5-second delayed prompt.

The team then ran short probe trials to see what really controlled the requests.

Sometimes the wanted item was missing, sometimes half-visible, sometimes fully in sight.

Each teen showed a different pattern. One asked only when the item was gone. Two asked only when the item was missing but other foods were visible.

All three always asked when the snack was right in front of them.

The cues that drove the requests were personal, not obvious.

Buskist et al. (1988) first showed that a 5-second delay can teach chained requests. G et al. built on that by asking, "What exactly is the learner now responding to?"

Rasing et al. (1992) used a similar reversal probe to check if odd gestures were true choices. Both papers prove you must test, not assume, what stimulus is in charge.

Kodak et al. (2009) compared two preference formats and also found idiosyncratic results. Together these studies warn: assessment format changes outcome.

If you think a learner is "asking for chips," run a quick probe: hide the chips, show only the bag, show the full item. The answer may surprise you and change your prompt plan.