In bilingual education, the integration of STE(A)M (Science, Technology, Engineering, Art, and Mathematics) with CLIL (Content and Language Integrated Learning) establishes a dynamic learning environment wherein students concurrently develop scientific, technical, linguistic, and creative competencies. These methodologies cultivate essential 21st-century skills, including collaboration, communication, and critical thinking. This investigation aims to accomplish two primary objectives: to develop a self-assessment rubric for integrating STE(A)M and CLIL methodologies and to validate this rubric utilizing the Delphi method. This research employs a mixed-methods approach, combining qualitative and quantitative techniques to develop and validate a self-assessment rubric for integrating STE(A)M and CLIL methodologies in bilingual education. The study was conducted in three phases: initially, the research team developed and refined the rubric through a comprehensive literature review to ensure it was grounded in theoretical frameworks and pedagogical practices. Subsequently, a panel of specialists was convened using the Nominal Group Technique to collaboratively design the initial rubric. Finally, the Delphi method was employed to validate and refine the rubric through two rounds of expert consultation, involving twelve academic professionals. The final rubric comprises 23 items, structured into two key dimensions: (1) the integration of STE(A)M and CLIL and (2) the design and planning of the teaching and learning process. The results indicate that the CLIL-STE(A)M-SAT rubric is a reliable instrument for assessing the integration of these methodologies. It demonstrates potential for future research and practical application by primary school educators in bilingual STE(A)M-focused contexts.