Flood disasters are prevalent and severely impact humans and the environment, with adolescents being particularly vulnerable. This study evaluated the "Get-Ready DEM," a tailored disaster educational module based on the Extended Parallel Pathway Model (EPPM), to enhance flood disaster preparedness among adolescents in Selangor, Malaysia. A two-arm, single-blinded, cluster-randomised controlled trial involved 287 adolescents from eight secondary schools, divided into intervention (140 participants) and control (147 participants) groups. The intervention group received the "Get-Ready DEM" once after the baseline assessment, while the control group was on the waitlist. Preparedness was measured using the Flood Disaster Preparedness Index (FDPI) scores at baseline, immediate post-intervention, and three months post-intervention. Data were analysed using a generalised estimation equation. Results showed a significant increase in FDPI scores for the intervention group immediately post-intervention (β = 2.15; 95% CI = 1.64, 2.65; p < 0.001) and at the three-month follow-up (β = 1.53; 95% CI = 0.96, 2.10; p < 0.001) compared to the control group. These findings underscore the EPPM framework's efficacy in designing effective flood disaster education. Implementing modules like "Get-Ready DEM" can significantly enhance adolescents' resilience and preparedness, suggesting a promising approach for disaster preparedness programs. This study was registered under Thai Clinical Trial Registry TCTR20240426001 on 26th April 2024 and obtained ethical approval by the Ethics Committee of Human Research University Putra Malaysia (JKEUPM-2022-858) and the Ministry of Education, Malaysia (KPM.600-3/2/3-eras (15189).