Children from about 5 years old may be able to use a Peak Flow Meter to record their PEFR. As one of the parameters by which we diagnose a severe or life-threatening asthma exacerbation is the percentage drop in PEFR, it would help to know what a child’s normal PEFR is! Click here for a guide of what you might expect for height. Children don’t always conform to these norms so it is important to know what the child’s own normal PEFR is; a 20% drop in their norm suggests poor control of asthma, a 40% drop suggests a significant exacerbation.