We asked whether the addition of PEF recordings to a symptom-based self-management plan improved outcome in school children with asthma. In an open-randomized, parallel-group, controlled trial, we studied children aged 7-14 years with moderate asthma. After a 4-week run-in, 90 children were randomized to receive either PEF plus symptom-based management or symptom-based management alone for 12 weeks. Thresholds for action based on PEF were 70% of best (for increasing inhaled steroids) and 50% of best (for commencing prednisolone). Children were asked to perform twice-daily spirometry at home (using an electronic recording spirometer that revealed only PEF to the study group alone) and to record a symptom diary. The mean daily symptom score was the main outcome. There were no differences between groups in mean symptom score or in spirometric lung function, PEF, quality of life score, or reported use of health services over 12 weeks. During acute episodes, children responded to changes in symptoms by increasing their inhaled steroids at a mean value of PEF of greater than 70% of best so that overall PEF did not contribute to this important self-management decision. Knowledge of PEF did not enhance self-management even during acute exacerbations.