This sequential explanatory mixed-methods study investigates the classroom assessment realities of novice EFL teachers in Iran’s public secondary schools—a context defined by large classes, limited resources, and the pervasive washback of the Konkur (university entrance examination). Drawing on Xu and Brown’s (2016) Teacher Assessment Literacy in Practice (TALiP) framework, the study integrates survey data (N = 158), semi-structured interviews (n = 20), and document analysis (n = 18 tests) to address three questions: the challenges teachers face in constructing classroom achievement tests; how teachers navigate between assessment principles from pre-service education and daily practical demands; and what supports teachers identify as critical for their development relative to current availability. Findings document a constrained assessment ecology where time scarcity (M = 4.62) was the most strongly endorsed challenge, and a triad of stakeholder accountability pressures—Konkur expectations, principal oversight, and parental demands—was consistently associated with assessment decisions. A substantial gap emerged between principle endorsement and implementation (e.g., formative assessment: 91.1% endorsement vs. 28.5% implementation), with constraint intensity negatively associated with implementation frequency (r = − .62). Four navigation approaches were identified: recalibrating priorities toward practicality, identifying manageable proxies for complex constructs, preserving communicative elements within examination-aligned formats, and developing localized knowledge through informal collegial networks—the last varying substantially by school location. Support priorities centered on structural investments—protected collaboration time, curated resources, and structured mentorship—where importance-availability gaps were substantial (e.g., collaboration time: gap = 3.14, d = 4.64). Findings challenge deficit-oriented interpretations by documenting that primary barriers are institutional rather than individual, carrying implications for teacher education and systemic support design in examination-driven settings.