The paper focuses on the development and evaluation of rubric used to assess STEM lesson plans. The rubric were constructed based on theoretical studies on STEM education and decision tree models to ensure objectivity and scientific rigor. Two experts in the field of STEM education independently used the rubric for assessment, and Cohen’s kappa coefficient was calculated to check the inter-rater reliability (k = 0.625), indicating a high level of agreement. The study also analyzed STEM lesson plans of teachers and pre-service teachers to identify the strengths and weaknesses of each plan. The results showed that the STEM lesson plans met the requirements of the guideline documents. Pre-service teachers’ lesson plans exhibited several strengths in terms of lesson plan ideas and the construction of inquiry-based activities, while teachers faced difficulties in identifying ideas and problem posing.