This prospective randomized controlled trial investigates the effect of ultrasound visual biofeedback as an adjunct to articulation therapy in children with speech sound disorders involving lingual targets. The intervention aims to facilitate acquisition of misarticulated sounds by providing real-time visualization of tongue movements. Participants are randomized 1:1 to immediate treatment or wait-list control, with stratification by disorder type, age, and gender where feasible. The wait-list control group continues usual care for 4 weeks before crossing over to receive the same intervention (ethical crossover design).

Inclusion Criteria:

• Primary diagnosis of speech sound disorder with errors on lingual target sounds
• Probe accuracy <70% on the primary target sound at baseline
• Cantonese as the first language
• Hearing thresholds ≤25 dB in at least one ear, with no hearing loss exceeding 50 dB in the other ear
• No syndromes or obvious dysmorphic features
• No language disorders associated with biomedical conditions (e.g., cerebral palsy, autism spectrum disorder)
• No oronasal fistula identified on oral examination or diagnosed velopharyngeal insufficiency

Exclusion Criteria:

• Presence of syndromes or dysmorphic features
• Language disorder associated with biomedical conditions (e.g., cerebral palsy, autism spectrum disorder)
• Hearing thresholds >25 dB in one ear and >50 dB in the other ear Planned surgical intervention during the study period

The dataset contains sensitive information from a small number of pediatric participants, including speech recordings, video-derived accuracy scores, and clinical details, which could risk re-identification even after de-identification. Sharing is restricted under our institutional ethics approval.