Other research has found that children who do better academically in kindergarten are more likely to go to college, get married, own homes and live in higher-income households.
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"Our findings provide compelling evidence for oral vocabulary's theorised importance as a multifaceted contributor to children's early development," said lead researcher Paul Morgan, associate professor of education policy studies at Pennsylvania State University in the US.
The researchers examined data from parental surveys reporting on the size of their children's vocabularies at two years of age.
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The researchers found that vocabulary gaps between groups of children were already evident by this early time period.
Females, those from more economically advantaged families, and those receiving higher quality parenting had larger oral vocabularies.
Children born with low birth weight or who were being raised by mothers with health problems had smaller vocabularies.
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When the researchers looked at how the children were doing three years later in kindergarten, they found that children with larger vocabularies at two years of age were better readers, knew more about mathematics, were more attentive and task persistent, and were less likely to engage in acting out- or anxious-type behaviours.
The findings appeared in the journal Child Development.
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