The goal of this study was to examine whether looking away behaviour of ADHD children interferes with their test performance. ADHD and normal children carried out two continuous performance tests (CPTs): one with a regular interstimulus interval (ISI), and the other with an irregular ISI. Children were instructed to push a response button when a target stimulus was presented on the monitor. The children's visual behaviour was recorded and scored offline. A micro-analysis of the visual behaviour indicated that ADHD children timed their looking away behaviour in the regular CPT: i.e. they looked away from the monitor and back in the interval between two succeeding stimuli. As a result they did not miss stimuli. Timing of looking away was less possible in the CPT with the irregular ISI. In this condition, looking away interfered with the ADHD children's task accuracy. In sum, looking away behaviour had a negative effect on the accuracy of test performance of ADHD children when stimuli were unpredictable. Looking away behaviour was not associated with the slower reaction times of the ADHD children. Hence, the often reported slowness of ADHD children is not to be explained by their visual behaviour.