Abstract Background For stroke treatment to be effective, it must be given as soon as possible. Delays are often caused by stroke bystanders failing to recognize symptoms and activate emergency medical services (EMS). This is especially a problem in socially excluded localities. This study evaluated the efficacy of a school-based intervention (HOBIT) in improving determinants and behavior intentions of EMS activation for suspected stroke in Czech socially excluded localities. Methods The quasi-experiment was conducted from May to June 2023 in the Moravian-Silesian region, Czechia. Schools were allocated to the intervention or control group (1:1). The HOBIT is a school-based intervention used to change health-seeking behavior when stroke is suspected. The primary outcome was the percentage change from the pretest to the follow-up test in the intervention group compared to the control group. The primary outcome was assessed in 4 domains: 1) knowledge, 2) behavioral intentions, 3) self-efficacy, and 4) outcome expectations. The intervention and control groups were compared using an unpaired t-test. Results We recruited 138 students aged 10-16 from 4 schools. The absolute differences in improvement between the control and intervention groups were 18% (95% CI 9-26, P < 0.001) for knowledge, 15% (95% CI 2-26, P = 0.01) for behavioral intentions, 6% (95% CI -4-15, P = 0.24) for self-efficacy, and 13% (95% CI 5-21, P < 0.001) for outcome expectations. The subgroup analysis showed that the intervention effect on self-efficacy, outcome expectations, and stroke behavior intentions was significant only in females. Conclusions The HOBIT improved stroke determinants and behavior intentions of EMS activation at schools in socially excluded areas. This study presents a health promotion practice that has the potential to improve stroke outcomes on a community level. It underscores the potential of school settings as an appropriate way to reduce health inequalities in socially excluded communities. Key messages • The HOBIT intervention improved determinants and behavior intentions of EMS activation for suspected stroke among students in socially excluded localities. • The study underscores the potential of school settings in reducing health inequalities and improving stroke-related outcomes in socially excluded localities.