The ability of teachers, social workers, police officers and laypersons (undergraduate and postgraduate students) to detect truths and lies told by 5–6 year-olds, adolescents and adults was tested in the present experiment. Lie detectors judged the veracity of statements from 18 liars and 18 truth tellers belonging to these three age groups. Accuracy scores were around 60% for each of these three age groups, both for detecting truths and for detecting lies. No occupational differences emerged. Moreover, judgements made by teachers, social workers and police officers showed an overlap, suggesting that an erroneous decision made by a member of one group may not easily be detected by a member of the other groups. The lie detectors were inclined to judge cues of nervousness, cognitive demand and attempted behavioural control as cues to deceit, even when truth tellers were displaying these cues.