Coalescing digital technologies into education has foregrounded gamified formative assessment (GFA) as a promising modality for advancing second language acquisition (SLA). The current study explored the effects of GFA on the writing proficiency of Iranian EFL learners, focusing on complexity, accuracy, and fluency (CAF). Employing a quasi-experimental design, intermediate and advanced learners were assigned to either gamified or traditional paper-based formative assessment conditions. Writing CAF performance was evaluated by estimating the mean of macro-constructs of complexity, accuracy, and fluency. Writing performance was analyzed using established CAF measures for complexity, accuracy, and fluency, based on widely recognized frameworks. To assess group and proficiency-level effects, key statistical tests, i.e., Friedman, mixed-design ANOVA, Kruskal-Wallis, Wilcoxon Signed-Rank, independent samples t-test, and Mann-Whitney U , were applied. The findings disclosed that GFA enhances writing proficiency, with the most substantial gains observed in complexity and fluency. Accuracy improvements, though evident, were more modest and varied by proficiency level: advanced learners improved more in complexity and fluency, whereas intermediate learners showed greater gains in accuracy. These results accentuate GFA’s pedagogical efficacy in fostering engagement, reducing cognitive load, and promoting self-regulated learning in writing instruction, offering crucial insights for language educators, curriculum designers, and digital assessment developers who aim to incorporate innovative, learner-centered assessment strategies.
