Studies investigating the feasibility and impact of mindfulness programs on emotional wellbeing when delivered by school teachers in pre-adolescence are scarce. This study reports the findings of a controlled feasibility pilot which assessed acceptability and emotional well-being outcomes of an 8-week mindfulness program (Paws b) for children aged 7–9 years. The program was delivered by school teachers within a regular school curriculum. Emotional well-being was measured using self-report questionnaires at baseline, post-training and 3 months follow-up, and informant reports were collected at baseline and follow-up. Seventy one participants aged 7–9 years were recruited from three primary schools in the UK (training group n = 33; control group n = 38). Acceptability of the program was high with 76% of children in the training group reporting ‘liking’ practicing mindfulness at school, with a strong link to wanting to continue practicing mindfulness at school (p < 0.001). Self-report comparisons revealed that relative to controls, the training group showed significant decreases in negative affect at follow-up, with a large effect size (p = 0.010, d = 0.84). Teacher reports (but not parental ratings) of meta cognition also showed significant improvements at follow-up with a large effect size (p =