This systematic review and meta-analysis investigated the efficacy of spelling interventions for the remediation of dyslexia and spelling deficits. Theoretically important moderators, such as the treatment approach as well as orthographic and sample characteristics, were also considered. Thirty-four controlled trials that evaluated spelling interventions in children, adolescents, and adults with dyslexia and spelling deficits were included. Results show that treatment approaches using phonics, orthographic (graphotactic or orthographic phonological spelling rules), and morphological instruction had a moderate to high impact on spelling performance. A significant influence of interventions that teach memorization strategies to improve spelling could not be confirmed. This work shows that understanding the principles of an orthography is beneficial for learners with dyslexia or spelling deficits and presents key components for effective spelling intervention.