Background/Objectives: School-Mindfulness-Based Interventions (SMBIs) have shown positive effects on children's mental health by enhancing emotional regulation and present-moment awareness. This pilot study explored the effects of an SMBI program on anxiety, depression, mindfulness, emotional awareness, executive functioning, and school well-being among French primary school students (mean age = 116 months; SD = 9.06). Methods: A quasi-experimental longitudinal design was employed, with assessments at pre-intervention (T1), post-intervention (T2), and follow-up (T3). Data were analyzed using repeated-measures ANOVA. Results: The study found no statistically significant changes across all assessed dimensions. The lack of significant results may reflect factors such as the program's duration, small sample size, reliance on self-report measures, and contextual challenges like the COVID-19 pandemic. However, slight numerical trends in anxiety and mindfulness scores suggest potential benefits that larger studies may better detect. Conclusions: While no significant improvements were observed, the findings highlight important considerations for SMBI implementation in schools in France and internationally. Future research should address current limitations by increasing sample sizes, employing multi-informant assessments, and integrating SMBIs with complementary approaches, such as social-emotional learning. Extending the program duration or incorporating booster sessions may enhance effectiveness. Embedding SMBIs into school curricula through a whole-school approach could foster the sustainable and impactful integration of mindfulness practices into daily school life.