Summer slide, uneven growth of academic skills during the calendar year, captures the fact that the learning gains children make during the school year do not continue at the same pace over the summer, when children are typically not in school. We compared growth of reading skills during the school year and during the summer months in children with prenatal or perinatal brain lesions (PL) and typically developing (TD) children from varying socioeconomic-status (SES) backgrounds as a new way to probe the role of structured environmental support in functional plasticity for reading skills in children with PL. Results showed that children with PL performed worse than TD children on both reading decoding and reading comprehension. Group differences were primarily driven by children with larger lesions and children with right-hemisphere lesions (RH). For reading comprehension, children with RH showed greater growth during the school year but more slide during the summer months than both TD children and children with left-hemisphere lesions, implicating a particularly strong role of structured input in supporting reading comprehension in this group. TD children from lower-SES backgrounds fell behind their TD peers from higher-SES backgrounds on decoding and reading comprehension but did not show differential patterns of school year and summer growth. Overall, results highlight the importance of considering the role of a host of factors interacting at multiple levels of analyses, including biological and environmental, in influencing developmental trajectories of TD children and atypically developing children.