This study directly investigates the pivotal question of whether teacher assessment practices are the primary drivers of student literacy. Utilizing 2021 Progress in International Reading Literacy Study (PIRLS) data from Iran, Finland, and Singapore, this cross-national analysis of fourth-grade students reveals a surprising finding: individual student factors (gender, socioeconomic status, and early home literacy activities) exert a far more pronounced influence on literacy scores than the assessment methods themselves. Despite examining a range of common practices—including observations, oral questioning, tests, and projects—the analysis demonstrates that these strategies largely lacked a consistent correlation with literacy performance, challenging conventional assumptions about their effectiveness. A notable exception was project-based assessment in Singapore, which demonstrated a significant positive relationship. The study ultimately reveals a surprising set of priorities: variables such as school emphasis on academic success and teacher gender were identified as more significant contributors to achievement than assessment techniques across the three diverse contexts. These findings advocate for a nuanced understanding of educational effectiveness that prioritizes student-level support and cultural context over a singular focus on assessment tool selection.