Two groups of children, one with good attention and one with poor attention, as rated by teachers, carried out a computerized visual search task. There were no differences between groups on an easy search for a single target, but when the task was made more difficult by including foils very similar to the targets or requiring alternating search for two different targets, the poor attention group made significantly more errors than the good attention group. The nature of these increases in errors was examined to discover whether they were due to errors specifically on the foils similar to the targets and errors due to failure to alternate. It was found that as well as making more errors of these types, the children with poor attention also showed a greater increase in other types of error (shape confusions, repetitions etc.) from the simple task to the more difficult ones. It is concluded that these findings do not support an explanation of poor attention solely in terms of weaknesses in specific executive functions, but suggest that supplementary or alternative explanations are needed, for example reduced processing capacity or problems in motivation or arousal when coping with difficult tasks.