Background <p>The potential for life-threatening allergic reactions in elementary schoolchildren has emerged as a major problem. There are, however, concerns about whether school nurses have the necessary competencies to respond to such emergency situations. This study developed simulation-based anaphylaxis training (SBAT) and online-based anaphylaxis training (OBAT) programs and compared their efficacy for improving elementary school nurses’ competencies in emergencies involving life-threatening anaphylactic events.</p> Methods <p>This is a quasi-experimental study. The sample comprised 40 and 47 elementary school nurses placed in the SBAT and OBAT groups, respectively. The effects of the intervention were analyzed using independent t-tests, Mann–Whitney U tests, Wilcoxon signed-rank test and analysis of covariance (ANCOVA)</p> Results <p>The pre-post differences were significantly higher in the SBAT group compared to the OBAT group in terms of knowledge (1.97 ± 1.21 vs. 0.87 ± 1.37; <i>p</i> &lt; 0.001), self-efficacy (7.50 ± 6.37 vs. 3.42 ± 4.47, <i>p</i> = 0.005), perceived performance competency in emergency care (4.11 ± 3.73 vs. − 0.76 ± 3.40; <i>p</i> &lt; 0.001), and critical thinking (7.02 ± 10.36 vs. 2.40 ± 8.03, <i>p</i> = 0.031). A within-group comparison of the SBAT group showed that all outcome measures significantly improved (<i>p</i> &lt; 0.001). However, in the OBAT group, only knowledge (<i>p</i> &lt; 0.001) and self-efficacy (<i>p</i> &lt; 0.001) significantly improved from the pretest.</p> Conclusions <p>Compared with OBAT, the SBAT program was more suitable for enhancing the perceived performance competency and critical thinking of elementary school nurses in emergency anaphylactic care. Therefore, school nursing trainers are advised to incorporate SBAT into continuing education programs for school nurses.</p>