This study was to develop an intervantion program of gifted underachievers at primary school and examine the effect of the program. An intervention program was devised based on research on the related literature, and programs for gifted underachievers currently employed in America. This program has been applied to 30 gifted underachievers at 4 primary schools and 31 at another 4 primary schools, and was proved to be practicable at primary schools in Korea from this preliminary experience. For statistical analysis a commercially available software (SPSS version 12.0) was used. Multi-level analysis using the growth model was done to analyze efficacy of the intervention program. The effect of the intervention program has been examined. Firstly, there was significant improvement in academic achievement as a result of the program. Secondly, gifted underachievers in this study showed optimistic changes in learning habit and attitude as a result of the program.