This study aimed to identify and elaborate Performance indicators that define and support meaningful assessment in Project-based learning (PBL), as perceived by experienced educators in Tehran. A qualitative research design was employed, utilizing semi-structured interviews to gather in-depth insights from 23 teachers, curriculum planners, and assessment specialists with extensive experience in PBL across various educational levels in Tehran. Purposeful sampling ensured diversity in participants’ backgrounds. Data collection continued until theoretical saturation was achieved. Interviews were transcribed verbatim and analyzed thematically using NVivo software, following Braun and Clarke’s six-phase approach to thematic analysis. Credibility was enhanced through peer debriefing, member checking, and reflexive journaling. Three overarching themes emerged as core domains of Performance indicators for meaningful assessment in PBL: (1) Authentic demonstration of learning, including realworld application, creativity, effective communication, collaboration, product quality, knowledge integration, and technology use,(2) Reflective and metacognitive skills, such as self-assessment, goal setting, evidence-based reflection, adaptability, critical thinking, and ownership of learning,and (3) Social and ethical responsibility, encompassing peer assessment, ethical conduct, community engagement, cultural awareness, and environmental consciousness. Illustrative quotations highlighted how these indicators manifest in practice and are valued by educators for supporting holistic student development. The study underscores the multidimensional nature of meaningful assessment in Projectbased learning, emphasizing the importance of integrating authentic, reflective, and socially responsible Performance indicators into assessment systems. The results have practical implications for educators, curriculum designers, and policymakers seeking to enhance the effectiveness and equity of assessment in PBL contexts.