<![CDATA[This study aimed to develop a testlet-based two-tier diagnostic test to identify students’ problem-solving difficulties in Newton’s Laws and to describe the profile of difficulties experienced by students based on Heller’s problem-solving stages. The study employed a Research and Development (R&D) method using the 4D model, consisting of the Define, Design, Develop, and Disseminate stages. The developed instrument was a two-tier diagnostic test comprising 20 items covering Newton’s First Law, Newton’s Second Law, Newton’s Third Law, and applications of Newton’s Laws. The instrument was administered to senior high school students, and the data were analyzed using the Rasch Model. The results indicated that the developed instrument met the validity and reliability criteria, with a person reliability value of 0.71, an item reliability value of 0.95, and a Cronbach’s Alpha value of 0.73. The item difficulty analysis showed that 30% of the items were categorized as very easy, 30% as easy, 15% as difficult, and 25% as very difficult. The analysis of students’ problem-solving difficulties revealed that the highest difficulty occurred at the check and evaluate stage (75%), followed by the plan a solution stage (60%), the visualize the problem stage (58%), the execute the plan stage (56%), and the describe the problem in physics terms stage (36%). These findings indicate that students still experience considerable difficulties in evaluating problem solutions and planning appropriate solution strategies. Therefore, the developed two-tier diagnostic test is suitable for identifying students’ problem-solving difficulties in Newton’s Laws.]]>
