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The influence of the place-value structure of the Arabic number ...

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<strong>The</strong>reby, <strong>the</strong> present data allowed for particularly pinpointing measures reflecting<br />

understanding <strong>of</strong> <strong>the</strong> <strong>place</strong>-<strong>value</strong> <strong>structure</strong> <strong>of</strong> <strong>Arabic</strong> <strong>number</strong>s for both tasks to be most<br />

relevant for <strong>the</strong> prediction <strong>of</strong> overall arithmetic performance in later numerical development.<br />

(iii) Finally, examining <strong>the</strong> <strong>influence</strong> <strong>of</strong> specific numerical effects in first grade (e.g.,<br />

compatibility effect, pure inversion errors) on corresponding effects in third grade arithmetic<br />

(e.g., carry effect, error rate in carry problems) revealed several meaningful interrelations.<br />

<strong>The</strong> size <strong>of</strong> <strong>the</strong> carry effect in third grade addition was predicted reliably by <strong>the</strong> first<br />

grade measure <strong>of</strong> CE functioning and <strong>the</strong> <strong>number</strong> <strong>of</strong> pure inversion transcoding errors: A<br />

higher <strong>number</strong> <strong>of</strong> pure inversion errors in first grade transcoding reliably predicted a more<br />

pronounced carry effect in third grade addition. Thus, flawed understanding <strong>of</strong> <strong>the</strong> <strong>place</strong>-<strong>value</strong><br />

positions <strong>of</strong> tens and units in first grade is related to difficulties in later arithmetic<br />

performance in additions requiring a carry operation in which correct integration <strong>of</strong> tens and<br />

units is essential. We suggest that both variables tap <strong>the</strong> same underlying concept <strong>of</strong> <strong>place</strong><strong>value</strong><br />

understanding in a basic numerical task in first grade (i.e., pure inversion errors in<br />

transcoding) as well as in a complex numerical task in third grade (i.e., addition involving<br />

carry over). <strong>The</strong>reby, <strong>the</strong> present data indicate that if <strong>the</strong> <strong>place</strong>-<strong>value</strong> concept is not mastered<br />

in early schooling difficulties in <strong>the</strong> successful application <strong>of</strong> this concept will evolve in later<br />

numerical development. To our knowledge, <strong>the</strong>se are <strong>the</strong> first longitudinal data which directly<br />

evidence <strong>the</strong> importance <strong>of</strong> early <strong>place</strong>-<strong>value</strong> understanding. Additionally, <strong>the</strong> CE component<br />

<strong>of</strong> WM was also positively correlated with <strong>the</strong> size <strong>of</strong> <strong>the</strong> carry effect: <strong>the</strong> better <strong>the</strong> CE in<br />

first grade <strong>the</strong> larger <strong>the</strong> carry effect in third grade indicating an <strong>influence</strong> <strong>of</strong> WM on complex<br />

addition which has previously also been observed in adults (e.g., Imbo et al., 2007a; 2007c).<br />

<strong>The</strong> regression model predicting <strong>the</strong> <strong>number</strong> <strong>of</strong> errors committed in carry addition<br />

problems incorporated three reliable predictors: a) <strong>the</strong> <strong>number</strong> <strong>of</strong> pure inversion errors in<br />

transcoding, b) visuo-spatial WM span and c) <strong>the</strong> size <strong>of</strong> <strong>the</strong> compatibility effect in <strong>number</strong><br />

comparison. So, children who had problems to identify tens and units successfully in<br />

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