Visual stress is the experience of unpleasant visual symptoms when engaged in reading and some other visual tasks. There is currently no objective diagnostic test for this condition, which affects a substantial proportion of the population and which can disrupt development of reading skills. The reliability of subjective reports of symptoms has been questioned, especially where children are concerned. Diagnosis by positive response to the preferred treatment method, either the sustained voluntary use of a coloured overlay or immediate improvement in reading rate when using an overlay, is usually regarded as the best option. Recent research has reported that children who are significantly impaired by a visually stressful pattern during reading-like visual search are more likely to show significant improvement in reading speed when using an overlay. This study was designed to evaluate a prototype computerised visual stress screener that incorporated visual search. The results confirmed that primary and secondary school children who were classified by the screener as having high susceptibility to visual stress had larger percent increases in reading rate with an overlay compared with those with low visual stress. The results also indicated that subjective reports of symptoms may not always be diagnostically effective with younger populations. It was concluded that screening for visual stress in reading using a computerised visual search task is an educationally promising development.