Shared book reading, and the conversation that accompanies it, can facilitate young children's vocabulary growth. To identify the features of extratextual questions that help 3-year-olds learn unfamiliar words during shared book reading, two experiments explored the impact of cognitive demand level, placement, and an approximation to scaffolding. Asking questions about target words improved children's comprehension and production of word-referent associations, and children with larger vocabularies learned more than children with smaller vocabularies. Neither the demand level nor placement of questions differentially affected word learning. However, an approximation to scaffolding, in which adults asked low demand questions when words first appeared and high demand questions later, did facilitate children's deeper understanding of word meanings as assessed with a definition task. These results are unique in experimentally demonstrating the value for word learning of shifting from less to more challenging input over time. Discussion focuses on why a scaffolding-like procedure improves children's acquisition of elaborated word meanings.

The effects of adult questioning on children's novel word acquisition during storybook reading were investigated. Three-year-olds were assigned to one of three conditions: vocabulary eliciting questions, noneliciting questions, and no questions (control). General vocabulary comprehension and novel word knowledge were equivalent across the groups before the storybook reading intervention. Children were read 3 storybooks repeatedly across 4 reading sessions and were tested for production and comprehension of novel words in the final session. Children's novel word comprehension increased more in both question conditions than in the control condition, suggesting that type of question is not as important to word learning as children's active engagement in discussion about novel words in general. Novel word production was not strongly affected by any of the reading conditions. However, asking children noneliciting questions did appear to foster production of new words more than not asking questions at all.

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2 categorization skills necessary for understanding hierarchies are the ability to form categories at different levels of generality and the ability to include the same objects into multiple categories. 2-year-olds appear to have the first skill, but some theoretical and empirical work suggests that the second may be a later acquisition. Yet, in 3 studies, 2-and 3-year-olds applied familiar basic level and superordinate labels to the same objects, even when reminded of basic labels before being tested with superordinates. They did not reserve superordinates for objects with unfamiliar basic level names (Study 2), and they were willing to apply superordinates to objects presented singly rather than in groups (Study 3). Thus, contrary to the implications of some previous work, 2-and 3-year-olds appear to have both of the categorization skills necessary for forming categorical hierarchies.

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