Empirical evidence supports the view that explicit teaching can make a positive difference to learning; however, further research is needed to understand the impact on learning to spell if spelling error analysis is used to inform explicit spelling instruction. This paper presents findings of an intervention study involving 572 students in Years 3 to 6 from 31 classes across four Australian schools. Fourteen teachers from two of the participating schools engaged in an intervention. This involved utilising spelling error analysis data to systematically plan and implement explicit and targeted spelling instruction. Sixteen teachers from the two comparison schools followed a "business-as-usual" pedagogy which appeared less targeted and explicit. Results indicate that all classes in the intervention group demonstrated a statistically significant improvement in spelling while only one comparison class demonstrated a statistically significant improvement. The promising findings highlight the power of using assessment-informed practices to explicitly teach spelling skills that are relevant to student needs.