The legitimacy of using the criterion of low reading achievement in the study of learning and memory skills with learning disabled children was assessed, based on a comparison of 35 nondisabled students, 15 low readers, and 10 learning disabled high school students. Learning disabilities were defined as encompassing perceptual and/or processing difficulties and a deficit in scholastic achievement of at least 3 years, while the low reading achievement category was distinguished by being at least 4 years below grade level. A series of 13 memory/learning tests and subtests was administered to each student individually in two or three 45 minute sessions. The findings indicated many similarities in the performance of learning disabled and low reading students, but also identified some significant differences between these two groups, particularly in tasks involving visual input and/or visual processing. Analyses of tasks where the two groups differed significantly always found the low reading group performing better than the learning disabled group, with no significant differences between the low readers and the nondisabled subject in each of these cases. While there was overlap between the low reading and learning disabled populations, the data suggest that there are enough differences to preclude using these populations interchangeably under the generic title "learning disabilities." It is concluded that there is a need to specify carefully the criteria used in sample selection, and to limit conclusions about research findings to the particular population studied. (SEW)