The present study examined underachievers' characteristics in reasoning etc. Sixty-four pairs of achievers and underachievers (5th-, 6th- and 7th- graders in public schools in Austin, Texas, U.S.A.) were the subjects. They were matched in sex, age, school year, IQ level and parents' socioeconomic status. Seventeen tests were given to them. Underachievers were low in deductive and inductive reasoning and number. Greater numbers of "wild guessers" as well as "careful unsuccessfuls" and lesser numbers of "steady Logical thinkers" and "intuitive thinkers" were found in underachievers. No significant differences were observed in perceptual and spatial ability, but the general tendency was that underachievers were rather better than achievers in perceptual speed and concrete manipulatable problems, but worse in such tests as require reasoning. Underachievers showed significantly poor ability in spontaneous flexibility, but no differences were observed in fluency. For immediate rote memory underachievers were not inferior to achievers, but were inferior qualitatively and quantitatively in associative memory and meaningful memory. Underachievers were also poor in reconstructing the previous stimulus-response combination. The data, thus obtained, confirm the hypothesis that underachievers are low in some aspects of thinking and memory, but, in some other aspects, have an almost equal level of ability as compared with that of achievers. In other words, underachievers show a rather unbalanced profile. It has been proposed that further studies and practical applications of teaching methods for underachievers should be based on the characteristics of underachievers' thinking and memory as found in this investigation.