Design methods should support engineers in efficiently developing technical systems but are often considered difficult to understand and apply. Conventional method validation focuses on performance outcomes, providing little insight into how users experience methods during application or adaptation. Structured reflection has been discussed to uncover misunderstandings and identify improvements, but its systematic application in method development remains underexplored. This article investigates how reflection can support design method adaptation in early validation. A multiple-workshop case study was conducted with 20 participants applying four methods under comparable conditions during the Product Architecture Design Summer School. Reflection was systematically planned, guided and analyzed through coded audios. The dataset includes four planning documents, 20 Canvas documents, 400 minutes of recordings and questionnaire feedback on reflection tools. Results show recurring reflection patterns: reflection is strongly process-oriented; action planning emerges only after descriptive phases ; social aspects are rarely addressed without explicit prompts. While reflection tools were perceived as useful, guiding questions require simplification for intuitive use. A four-stage framework for Reflection-Driven Method adaptation is proposed, supporting researchers in planning, executing and analyzing reflection as a method validation instrument. The study demonstrates how reflection can produce actionable improvements and offers a reproducible approach for early method validation in engineering design.
