<![CDATA[This research was motivated by the presence of learning obstacles among first-grade elementary school students in addition and subtraction operations for numbers 1–20, such as misunderstandings of operational meanings, difficulties with counting-on strategies, procedural hurdles, and challenges in translating word problems. This study aims to identify these learning obstacles, as well as to design and implement a hypothetical didactical design based on the Hypothetical Learning Trajectory (HLT) to minimize these obstacles. The research method employed is Didactical Design Research (DDR), which comprises three main phases: prospective analysis, metapedadidactic analysis, and retrospective analysis. The subjects of this study were 22 first-grade students at SD Negeri 17 Lahat. Data collection techniques included diagnostic tests, prerequisite ability tests, teacher and student interview guides, and analysis of textbooks as well as learning instruments. The results of the prerequisite test analysis revealed that the most dominant obstacles occurred in the concept of subtraction/remainder (31.8%), solving word problems (40.9%), and the concept of addition combination (22.7%). Based on these obstacles, the researcher designed a didactical framework utilizing concrete media such as fruit-themed ice cream sticks, visual images, and number lines to bridge the transition of students' thinking from the concrete to the abstract phase. The final post-implementation identification test results showed a significant reduction in the quantity of students' learning obstacles (with only 1 to 2 students remaining affected). Consequently, the developed didactical design proven to be effective and feasible for use as an alternative learning approach to minimize learning obstacles in addition and subtraction operations of numbers 1–20 for first-grade elementary school students.]]>
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