Wolraich, Wilson, and White (1995) conducted an extensive and thorough review of 16 double-blind, placebo-controlled studies evaluating the effects of sugar on child behavior. Participants included normal children, children identified by parents as behaving poorly after sugar ingestion, children with diagnosed hyperactivity or ADHD, and aggressive, delinquent children. Measures focused primarily on the behavior of children with ADHD and used behavior-rating scales completed by parents and teachers (along with neuropsychological measures) to assess vigilance, impulsivity, memory, and motor skills. In spite of considerable variation in subjects, challenge agents, and dependent measures, the results were remarkably consistent.
Findings did not support the hypothesis that refined sugar affects hyperactivity, attention span, or cognitive performance of children, although the possibility of an effect on a subset of children could not be ruled out.
It is interesting to note that despite presentation of clinical evidence to the contrary, many participating parents remained convinced of an association between sugar and adverse behavior.
http://www.medscape.com/viewarticle/558797_6