Rapid automatized naming (RAN) is widely used to identify reading disabilities (RD) and has recently been considered a potential predictor of risk for mathematics learning disabilities (MLD). Here we longitudinally examine RAN performance from Grades K to 8, to view how growth on RAN response time differs for children with RD versus MLD. Across all participants, there was significant stability of RAN performance for all three subtests. For all three subtests, there was significant between-child variability in response times (RTs) at kindergarten and Grade 8; for select combinations of subtests, there was also between-child variability in difference scores over time. Relative to typically achieving peers, children with MLD or RD were slower on all three subtests at kindergarten, but these deficits were most pronounced for children with MLD versus RD at kindergarten and more persistent through Grade 8 for children with RD. RAN numbers and letters performance was closely related in the RD group, more so than in the MLD group, despite deficits on both subtests across groups. Our findings indicate that empirically guided modifications of RAN are needed for extending its use for evaluating risk for MLD.