When choosing a focus, a GBS designer must first decide whether the mission is best served by having the student pursue a design, control, discovery, or explanation task (or some combination of these). This decision leads to the establishment of the iterative sequence for the GBS; that, in turn, dictates how the instructional elements of the GBS are to be paced and sequenced.
Each class of focus task carries with it a natural iterative sequence (that is, a natural sequence of steps that people follow when performing the task). For a GBS with a design focus, the student repeatedly generates a part, integrates it into the whole, then tests the whole. If the focus is explanation, the student might conduct a test, observe it, then produce an explanation. Observing phenomena and stripping it down to necessary and sufficient conditions is central to a discovery task. A control-based GBS inevitably revolves around decisions: detect a state of affairs, gather evidence, then choose between alternative plans.
Creating a Cover Story for a GBS
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