Purpose: Children make spelling errors despite classroom instruction on phoneme-grapheme connections and spelling rules. We examined whether additional practice helps to decrease the number of spelling errors for a morphological spelling rule. We distinguished explicit practice in applying a spelling rule from implicit exposure to correct word forms. Method: After a dictation task, Dutch second graders (n = 139; 46.8% girls) were matched and randomly divided over explicit, implicit, and no-additional practice conditions. Additional practice was based on evidence-based exercises and encompassed five sessions. The dictation task included target words that were practiced, as well as transfer words that were not. Results: Both explicit and implicit practice resulted in better performance on target words (large effect) as well as transfer words (medium to large effect) compared to no-additional practice. There were no differences between implicit and explicit practice. Conclusion: These findings indicate that spelling performance can be improved by additional practice, both by telling and showing. Using evidence-based explicit or implicit exercises after classroom instruction has taken place can (further) improve children's spelling of rule-based words.