The extent to which reading achievement is causally impacted by eligibility for special education services due to a learning disability (LD) or speech or language impairment (SLI) is currently unclear. In this registered report, we analyzed U.S. national data from the Early Childhood Longitudinal Study--Kindergarten Cohort of 2010-2011 (ECLS-K: 2011) using student-fixed effects with a lagged dependent variable estimated by maximum likelihood to assess (a) whether being assigned an Individualized Education Program (IEP) and so receiving special education services affects individually measured reading achievement for students with LD or SLI (N = 2,400) and (b) heterogeneity in the effect of having an IEP for different demographic groups. We observed small, negative effects in early grades (d = -0.09) but larger, positive effects in later grades (ds = 0.29-0.67). These more negative early effects primarily occurred among students identified with SLI, male students, and students who faced socioeconomic barriers. Effects were more positive for students who are Black, Hispanic, or who exited special education.