There has been a growing emphasis on understanding the links between children’s social characteristics and academic achievement. Socio-emotional characteristics linked with academic performance are known as learning-related social skills (LRSS). Prior research has mostly examined the links between LRSS in early childhood and short-term assessments of academic achievement. More recent studies have begun to examine trajectories of achievement, but they have primarily been linked with early LRSS. Given that children interact with several potential socializing agents such as teachers and peers when they are in school, links between middle childhood LRSS and academic trajectories require attention. In this study, links between three indices of LRSS (attention, self-regulation, and behavior problems) and trajectories of reading, vocabulary, and math were examined from first through fifth grade. Early LRSS and demographic factors were also considered. It was expected that between-children differences in middle childhood attention problems, self-regulation, and behavior problems would be associated with average levels of achievement and growth over time. Within-child changes in attention problems, self-regulation, and behavior problems were also expected to be associated with changes in achievement. Another goal of the study was to examine whether LRSS moderated the links between family income and achievement and between gender and achievement. It was expected that having higher LRSS would be associated with a lower risk of poor achievement for children from low income families and for boys. Using HLM 6.03, these links were tested in a subset of the data from the NICHD SECCYD (n = 1123). Missing data were imputed by subgroups of race/ethnicity. Between-children differences on teacher-reports of attention problems displayed significant negative links with the average levels, but not with the slopes, of reading, math, and vocabulary. Early LRSS were better predictors of the intercepts of achievement but not after taking demographic factors into account. Within-child changes in LRSS during middle childhood were not significantly associated with changes in achievement. Interactions between poverty and LRSS were also not significant. However, higher levels of teacher-reported attention problems were associated with higher levels of math scores for girls. Implications and directions for future research are discussed.