We presented a design-based study within the context of a four-session Scratch programming activity among 23 fourth-grade students in Hong Kong. Inspired by the computational thinking (CT) strategies and the 5E instructional model, we investigated students’ mathematical learning of fractions in a Scratch (block-based programming) environment. Students developed CT concepts, practices, and perspectives by building a “fraction magic calculator” in groups. This study analyzed the lesson design, students’ drawings, interviews, and work expressing their mathematical understanding of fractions in Scratch applications. The learning tasks were designed to support the students’ fraction learning and utilized computational abstractions in the form of variables, functions, and iterations to formulate mathematical models in a programming context. Students’ artifacts and feedback showed they were interested in learning fractions in a programming learning context, contributing to exercising and improving their fraction concepts and CT. Ultimately, we emphasized the benefits of CT integrated into mathematics education, promoting students’ understanding of fraction concepts, a set of CT abilities (concepts, practices, perspectives), and learning motivation. Moreover, we suggested a set of non-cognitive skills (e.g., socializing, expressing) to enrich the CT perspectives in the framework and show the importance of developing coding communities to co-create digital artifacts among learners. Overall, we highlighted that mathematics teachers should apply and create learning tasks that promote computational thinking to forge mathematical ideas and thinking. Copyright © 2023 The Author(s).