The purpose of this study was to investigate the relationship between the development of children's selective attention strategies and the efficiency of inhibitory mechanisms. Recently the research by Miller et al. suggests a developmental lag between producing a strategy of selective attention and benefiting from it. The possible explanation for the developmental lag is that allocating effort to produce a strategy reduces the processing capacity available for recall per se. This view was presently related with a generic resources hypothesis. But recently Hasher and Zacks(l988) proposed inefficient inhibition hypothesis that, with aging, inhibitory processs become less efficient, resulting in irrelevant information entering and being maintaind in working memory. We propose an extention of their model to account for developmental differences in children's recall task performence, with the added assumption of limited, generic resources. That is, inhibitory mechanisms become more efficient over childhoood, resulting in less irrelevant information entering working memory with age, yielding increased processing efficiency and increased funtional capacity of working memory. If then, that one of the causes of the develomental lag will be inefficient inhibitory mechanisms will be hypothized. From this point of view, the following two hypotheses concerning the relationship between the development of children's selective attention strategies and the efficiency of inhibitory mechanisms. H.1 : Even if children spontaneously use an externally perfect selective attention strategies, there will be significant differences in the interference effect showing the efficiency of inhibitory mechanisms between high group children who got higher scores and low group children who got lower scores on the recall tasks. H.2 : Even if children spontaneously use an externally perfect selective attention strategies, there will be significant differences in the suppression effect showing the efficiency of inhibitory mechanisms between high group children who got higher scores and low group children who got lower scores on the recall tasks. To test the above hypotheses, an experiment was conducted. 40 children of 3rd and 4th grade respectively were assigned into two groups of the same number, high and low groups, according to their pretest scores. All the children were tested individually by Stroop tasks which consist of three conditions, Neutral, Stroop Control, and Ignored Repetition. The interference effect was observed by comparing conditions Neutral and Stroop Control. The suppression effect was observed by contrasting Ignored Repetition with Stroop Control condition. The data obtained by these tasks were analyzed using MANNOVA, Wilcoxon test, and Mann-Whitney test. The result of the experiment was as follows. There was significant difference in the interference effects and the suppression effects showing the efficiency of inhibitory mechanisms between high and low group children which had been divided according to the recall task score. Considering the result of the experiment, the following conclusions could be made. First, there is significant difference in the efficiency of inhibitory mechanisms between the high and low group children which were divided according to the scores of recall tasks. Second, one of the causes of the develomental lag of selective attention atrategy is inefficient inhibitory mechanisms. Finally, it is thought that the inefficient inhibition hypothesis could be applied to child cognitive development.