Postprint manuscript and supplementary materials for the below project: Peterson, L., Savarese, C., Campbell, T., Ma, Z., Simpson, K.O., & McAllister, T. (2022). Telepractice treatment of residual rhotic errors using app-based biofeedback: A pilot study. *Language, Speech, and Hearing Services in Schools.* https://doi.org/10.1044/2021_LSHSS-21-00084 *Purpose*: Although mobile apps are used extensively by speech-language pathologists, evidence for app-based treatments remains limited in quantity and quality. This study investigated the efficacy of app-based visual-acoustic biofeedback relative to non-biofeedback treatment using a single-case randomization design. Due to COVID-19, all intervention was delivered via telepractice. *Method*: Participants were four children aged 9-10 with residual errors affecting American English /ɹ/. In a single-case randomization design, individual sessions were randomly assigned to feature practice with or without biofeedback, all delivered using the staRt app. Progress was assessed using blinded listener ratings of word probes administered at baseline, post-treatment, and immediately before and after each treatment session. *Results*: All participants showed a clinically significant response to the overall treatment package, with effect sizes ranging from moderate to very large. One participant showed a significant advantage for biofeedback over non-biofeedback treatment, although the order of treatment delivery poses a potential confound for interpretation in this case. *Conclusions*: While larger-scale studies are needed, these results suggest that app-based treatment for residual errors can be effective when delivered via telepractice. These results are compatible with previous findings in the motor learning literature regarding the importance of treatment dose and the timing of feedback conditions.