Measures designed to test two components of attention (decison making and maintaining attention over time) were studied in 36 educably mentally retarded (EMR) boys at three age levels (10, 13, and 14 years). Multivariate analyses, followed by univariate and paired comparison tests, indicated that both EMR and normal Ss increased in attentional efficiency with age in both attentional processes. Findings suggested that at about 12 years of age, the capacity for most attentional processes has already developed in both EMR and normal children. Lack of difference between EMR and normal Ss on the attention components was interpreted as supporting the developmental position of retardation. Correlations between the two attentional measures were not significant, further supporting the interpretation that the hypothesized components of attention represent independent influence on children's academic performance. (Author)