Figure 1.

Flow diagram of the progress of schools and children through the trial. ¹ Includes all children in school years 1 to 6 (generally aged from five to eleven). ² 'Follow-up children' are a randomly selected sample of "All children", whose parents are followed up for detailed information about their illness absences. The primary outcome, absence episodes due to illness, is only measured on this group of children. Figure adapted from Campbell [30].