The primary objective of this study was to develop and evaluate a scientific modeling skill assessment for grade 6 students in Thailand. The assessment comprised three test components: a multiple-choice test, a matching test, and a written test, which underwent rigorous evaluation through three trial processes. A total of 370 participants were randomly selected from 29 schools in a province of Thailand using a multi-stage random sampling method. The results demonstrated that the developed assessment exhibited appropriate content validity, difficulty, discrimination, and reliability. Additionally, the assessment provided a means to determine students' levels of scientific modeling skills, ranging from very high to limited. By addressing the absence of systematic assessments specifically designed for Thai students, this study fills a significant gap in the Thai educational context. The practicality and scalability of the assessment make it suitable for implementation with a larger number of participants. However, it is important to acknowledge the limitation of the study's relatively small sample size. Future research endeavors should aim to replicate the study with a more diverse and extensive sample to enhance the generalizability of the findings. Overall, this project contributes to the field of scientific modeling skill assessment and offers valuable insights for promoting and evaluating students' scientific modeling skills in the context of grade 6 education in Thailand.