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2013 Conference Proceedings - University of Nevada, Las Vegas

2013 Conference Proceedings - University of Nevada, Las Vegas

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Figure 2. (A) P3. (B). Extension <strong>of</strong> P3 to P4. (C) Final explanation for P4iterating composite units, etc.) are a step toward identifying what, in the GLP metaphor,constitute the genetic material <strong>of</strong> the thinking involved, but these do not address the way thisthinking evolves or comes into being. While we need these classifications, they do little to moveany student forward in his or her thinking without some concept for how new ideas can grow anddevelop. One <strong>of</strong> Steffe’s subjects, Tyrone, provides a powerful example for the way thinkingworks in our metaphor. Tyrone clearly has a sense <strong>of</strong> multiplication as repeated addition, anddemonstrates this through his initial step-counting by units <strong>of</strong> 20 to determine 20 × 20. Whenasked to calculate 30 × 20, he starts from his previous answer to 20 × 20 and step-counts foranother 10 groups <strong>of</strong> 20. The numbers he has encountered allow him to use an existing strategy(step-counting) to solve two very similar problems; he clearly understands that 30 × 20 = (20 +10) × 20 = 20 × 20 + 10 × 20 on an intuitive level. Tyrone is demonstrating problem solvingabilities that are inherent in the ability to mutate an existing solution strategy. Because this wassuccessful, Tyrone will now be encouraged to continue finding ways to adapt this strategy.Although all new student ideas are formed from prior understandings, like natural evolution,GLP does not always produce successful strategies. The fossil record shows events, like theCambrian Explosion (Gould, 1990), that have left their mark in the Burgess Shale, showing ahuge variety <strong>of</strong> evolutionary solutions, none <strong>of</strong> which are found in today’s natural world. Thesame is true for GLP. Van Dooren, deBock and Verschaffel (2010) provide copious examples <strong>of</strong>students hybridizing existing strategies to produce new strategies that are then casually dropped.Their study looked at how 3 rd – 5 th graders handled problems that were either additive ormultiplicative in structure, having either integer ratios or non-integer ratios. Younger students<strong>Proceedings</strong> <strong>of</strong> the 40 th Annual Meeting <strong>of</strong> the Research Council on Mathematics Learning <strong>2013</strong> 194

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