Cohort effects concern the impact of being born in one particular historical context rather than another

Around what age are most children fully capable of engaging in fluent conversation with speakers of any age?

A) 6 B) 9 C) 11 D) 7

The most likely explanation for the widespread scatter in subtest scores on tests such as the WISC is

a) lack of ability b) some clinical disorder c) low levels of subtest reliability d) incorrect scoring