The present study investigated responsiveness to intervention in children with an earlier versus later diagnosis of dyslexia. We examined differences between second (n=122; early diagnosis) and third (n=158; late diagnosis) graders with dyslexia on reading and spelling abilities before, during and after a dyslexia intervention as well as in precursor measures. Scores were also compared with those of typical reading peers at second (n=108) and third (n=119) grade. Finally, we examined the role of second versus third grade diagnosis in the prediction of variation in responsiveness to intervention. Before the intervention, the early diagnosed group was behind the late diagnosed group on almost all measures. During the intervention, the earlier diagnosed group made more progress on word decoding accuracy and showed comparable progress in skills otherwise. The effect of the intervention was indicated from the fact that later diagnosed children before the intervention were behind earlier diagnosed children after the intervention--when at a comparable age--on all reading and spelling measures. Finally, we showed that an early or later diagnosis of dyslexia similarly predicts the growth of reading and spelling outcomes with only a small benefit of early diagnosis for pseudoword reading efficiency.