In children with speech sound disorder, deficits in spoken communication pose a barrier to academic and social participation. Of particular concern is the subset of children who exhibit atypical speech patterns that persist past the age of 9, termed residual speech errors (RE). Research to date has not established why speech errors resolve in some children but persist in others, and effective forms of intervention for RE have remained elusive. This gap gives rise to a long-term goal of establishing evidence-based therapy guidelines for RE while identifying factors that cause and maintain these errors. This study will focus on the subset of children with RE affecting the phoneme /r/ (RE-/r/). The first aim of this proposal is to compare treatment effect sizes produced by two forms of treatment for RE, acoustic biofeedback therapy and traditional articulatory therapy. Preliminary studies have shown that some children can eliminate RE using acoustic biofeedback (a dynamic visual representation of the speech signal), but the efficacy of biofeedback therapy for RE has never been evaluated with systematic experimental methods. To test the hypothesis that biofeedback therapy yields greater treatment gains than traditional therapy, both methods will be applied concurrently to different /r/ targets in an alternating treatments design with multiple baselines across behaviors. 16 children with RE-/r/ will complete 10 weeks of individual therapy. Aim 2 of this proposal will draw on principles of motor learning to explain how biofeedback can succeed in changing articulatory patterns that do not respond to other forms of practice. One hypothesis holds that errors persist when the speaker's internal auditory target for a sound is incorrect, and that biofeedback is effective because it provides knowledge of performance (KP) feedback to guide the speaker to a more accurate target. However, KP feedback has been shown to lose its advantage when the target is already well- specified. Therefore, the working hypothesis for Aim 2 is that children with a poorly specified auditory target for /r/ (i.e., poor perception of /r/) wll derive greater relative benefit from biofeedback therapy than children with good perception. To test this hypothesis, pre-treatment perceptual sensitivity will be measured with a synthetic 10-step acoustic continuum from /r/ to /w/, and the correlation between this measure and the difference in effect sizes calculated in Aim 1 will be evaluated. A significant negative correlatio, indicating that the advantage for biofeedback over traditional therapy is greater in children with poor perception, is anticipated. This research will be clinically significant because the results o Aim 1 will have immediate implications for the selection of therapy methods, and the results of Aim 2 will help clinicians match clients to the most appropriate therapy approach based on their individual characteristics. This study will also be theoretically significant because it is the firt to systematically apply principles of motor learning to investigate the mechanism by which biofeedback influences articulatory skill in children. In the long term, these findings will be par of a continuum of research that will illuminate the causes of RE while continuing to identify principles of intervention for the disorder.