Researchers have noted a nonlinear association between reading instruction dosage (i.e., hours of instruction) and reading outcomes for Grade K-3 students with reading difficulties (K-3 SWRD). In this article, we propose a nonlinear meta-analysis as a method to identify both the maximum effect size and optimal dosage of reading interventions for K-3 SWRD using 26 peer-reviewed studies including 186 effect sizes. Results suggested the effect sizes followed a concave parabolic shape, such that increasing dosage improved intervention effects until 39.92 hours of instruction (d[subscript max] = 0.77), after which the intervention effects declined. Moderator analyses found that maximum intervention effects on fluency outcomes were significantly larger (d[subscript max] = 1.34) than the overall maximum effect size. Also, when students received 1:1 instruction, the dosage response curve displayed a different functional form than the concave parabolic shape, showing the effect increased indefinitely after approximately 16.8 hours of instruction. Implications for research and practice are discussed.