Background: In children with a cleft palate with or without a cleft lip (CP±L), some evidence exists for superior results of high-intensity speech intervention (HISI) compared with low-intensity speech intervention (LISI) on speech and health-related quality of life (HRQoL). However, the existing research often involves small sample sizes. Additionally, therapy in these studies is typically administered by researchers with extensive experience in treating speech disorders in these children. In contrast, first-line speech--language pathologists (SLPs) often possess considerably less experience in treating these children and clinical practice is subject to a wider array of environmental influences. Moreover, there are insufficient data on the cost-effectiveness of HISI compared with LISI. So far, these factors have hampered the implementation of HISI in clinical cleft practice. Aims: The purpose of this study is twofold: (1) to compare the effectiveness of HISI and LISI on a larger societal scale, as delivered by first-line SLPs, on speech and HRQoL in Belgian Dutch-speaking children with a CP±L; and (2) to evaluate the cost-effectiveness. Methods & Procedures: This study consists of a large-scale, longitudinal, two-centre randomized controlled trial to investigate the effectiveness of HISI and LISI. Children with a CP±L, aged between 4 and 12 years, are randomly assigned to one of the two intervention groups. A sample size calculation determined that 35 participants per group are needed to ensure adequate statistical power. Children in the HISI group will receive intervention with a session duration of 30 min, a dose frequency of five sessions per week and a total intervention duration of 8 weeks (two 4-week blocks with a rest period of 12 weeks). Children in the LISI group will receive intervention with a session duration of 30 min, a dose frequency of two sessions per week and a total intervention duration of 20 weeks. The cumulative intervention intensity is kept constant. Each child will receive identical phonetic--phonological speech intervention provided by first-line community SLPs in private practices. Speech samples and patient- and caregiver-reported outcome measures will be collected on multiple data points before, during and after the intervention period. The cost-effectiveness will be evaluated by applying a cost-effectiveness and cost-utility analysis. Outcomes & Results: It is hypothesized that HISI will lead to superior speech outcomes in terms of consonant production and proficiency, resonance, speech understandability and speech acceptability, as well as improved HRQoL compared with LISI. Additionally, HISI is expected to be cost-effective compared with LISI. Conclusions & Implications: This project contributes to the development of evidence-based clinical practice guidelines regarding speech intervention intensity in children with a CP±L.