["Measuring children's dietary behavior is central to evaluating interventions and identifying predictors and outcomes of dietary behaviors. Systematic biases may obscure or inflate associations with self-reported intakes.", "To identify cognitive, behavioral, and social correlates of bias in children's reporting of breakfast items on a self-completion questionnaire.", "Cross-sectional survey. Children completed standardized tests of episodic memory, working memory, and attention, and a questionnaire assessing attitudes toward breakfast. Teachers completed a classroom behavior measure. Associations between measures and children's underreporting of breakfast foods (ie, cereals, bread, milk, fruits, sweet items, and potato chips) on a self-completion questionnaire relative to validated 24-hour recall were examined.", 'Subjects were aged 9 to 11 years (n=678). Data were collected from 111 schools throughout Wales in 2005.', 'A larger percentage of less-healthful breakfast items (ie, sweet snacks and potato chips) than more healthful items (ie, fruit, cereals, bread, and milk) were omitted from questionnaire self-reports. Children from lower socioeconomic status schools omitted more items than those from wealthier schools (Kruskal-Wallis H=12.51, P<0.01), with omissions twice as high for less-healthful items than for more-healthful items within the lowest socioeconomic status schools. Those with positive attitudes (H=23.85, P<0.001), better classroom behavior (H=6.26, P<0.05), and better episodic memory (H=8.42, P<0.05) omitted fewer items than those with negative attitudes, poorer behavior, and poorer episodic memory. Children who ate more items omitted more than those who ate fewer (H=47.65, P<0.001). No differences were observed in terms of attention and working memory.'] Are cognitive , behavioral , and social factors associated with bias in dietary questionnaire self-reports by schoolchildren aged 9 to 11 years?