This study investigated the efficacy of a 2-week mindfulness-based intervention aimed at reducing stress among teachers. The intervention involved a self-guided program consisting of daily reflective journaling and three times-weekly assigned readings from a mindfulness training book tailored for teachers. Sixty Iranian teachers were divided into an experimental group and a control group, with the latter receiving the intervention post-study. Stress levels were measured using the Perceived Stress Scale (PSS) at three points: pre-intervention, immediately post-intervention, and 5 weeks post-intervention. Mixed ANOVA analyses indicated a significant effect of time on stress levels (Wilks' Lambda = 0.896, F (2, 57) = 3.306, p = 0.044, partial [eta-squared] = 0.104). Immediately post-intervention, the experimental group showed a small, nonsignificant reduction in stress compared to the control group (Cohen's d = 0.08, p = 0.742). However, at the 5-week follow-up the experimental group reported a moderate, statistically significant reduction in stress compared to the control group (Cohen's d = 0.60, p = 0.023), indicating sustained intervention effects. Qualitative data from interviews and reflective journals revealed three main findings: (1) development of mindfulness awareness, (2) gradual impact on stress management, and (3) sustained stress reduction and integration of mindfulness. These themes highlight the initial skepticism, the progressive understanding and application of mindfulness, and the lasting integration of these practices into daily teaching and personal life. Findings suggest that even brief mindfulness interventions can lead to significant, sustained reductions in perceived stress among teachers. This study confirms the benefits of mindfulness interventions on teachers and sheds light on the underlying processes contributing to these benefits.