Reading comprehension is a critical skill for EFL learners, yet the effectiveness of instructional strategies may vary depending on learners' individual differences, including their cognitive tempo. This quasi-experimental study examined whether concept mapping differentially benefits Iranian impulsive and reflective EFL learners' immediate and long-term reading comprehension. Eighty-one male intermediate learners (aged 16–20) in Alvand, Qazvin, during the 2025–2026 academic year were assigned to Reflective (n = 27), Impulsive (n = 27), and Control (n = 27) groups. The two experimental groups received an eight-session concept mapping intervention; the control group followed conventional instruction with no concept mapping practice. Reading comprehension was assessed via a 40-item multiple-choice immediate posttest and a four-week delayed reading comprehension test. Concept maps were scored for structural quality. ANCOVAs controlling for pretest showed that the Reflective group significantly outperformed the Impulsive group on the immediate posttest (adjusted M = 16.0 vs. 15.0, p = .012, d = 0.73) and the delayed posttest (adjusted M = 12.5 vs. 10.5, p = .018, d = 0.68); both experimental groups outperformed the control group. Bootstrapped mediation analyses indicated that map quality partially mediated group differences on both immediate (indirect effect β = 0.52, 95% CI [0.19, 0.94]) and delayed (β = 0.48, 95% CI [0.16, 0.87]) comprehension. Results demonstrate that the effect of concept mapping is moderated by cognitive tempo and that map quality serves as a mechanism driving both immediate and long-term comprehension gains. Differentiated scaffolding is recommended for impulsive learners.