Purpose: Early auditory experiences are fundamental in infant language acquisition. Research consistently demonstrates the benefits of early intervention (i.e., hearing aids) to language outcomes in children who are deaf and hard of hearing. The nature of these benefits and their relation with prefitting development are, however, not well understood. Method: This study examined Ontario Infant Hearing Program birth cohorts to explore predictors of performance on the Preschool Language Scale--Fourth Edition at the time of (N = 47) and after (N = 19) initial hearing aid intervention. Results: Regression analyses revealed that, before the hearing aid fitting, severity of hearing loss negatively predicted 19% and 10% of the variance in auditory comprehension and expressive communication, respectively. After hearing aid fitting, children's standard scores on language measures remained stable, but they made significant improvement in their progress values, which represent individual skills acquired on the test, rather than standing relative to same-age peers. Magnitude of change in progress values was predicted by a negative interaction of prefitting language ability and severity of hearing loss for the Auditory Comprehension scale. Conclusions: These findings highlight the importance of considering a child's prefitting language ability in interpreting eventual language outcomes. Possible mechanisms of hearing aid benefit are discussed.