<![CDATA[Mathematics remains underrepresented in integrated STEM practice, and ratio and proportion, despite lending itself to authentic design tasks, is a topic students persistently struggle to master, with no prior development research combining a paper bridge project and a student-built IoT weight scale to teach it. This study developed and examined the content validity of a STEM-PjBL learning tool, comprising a teaching module, student worksheet, and assessment instrument, that integrates a paper bridge project with a student-built IoT weight scale to teach ratio and proportion to seventh-grade students through a six-phase Engineering Design Process (Ask, Research, Imagine, Plan, Create, Improve). Using a Research and Development approach limited to the Analysis, Design, and Development stages of the ADDIE model, the initial draft was validated by two mathematics education lecturers and analyzed using Gregory's content-validity formula. All three components, teaching module, student worksheet, and assessment instrument, achieved a validity index of 1.00 across all rated aspects, placing them in the high-validity category, and were subsequently revised based on the validators' qualitative feedback. These findings indicate that the developed STEM-PjBL tool is content-valid and ready for classroom trial, offering a concrete model for embedding authentic, student-generated data into mathematics instruction and narrowing the disciplinary gap between IoT-based STEM tools and mathematics learning.]]>
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