The effects of randomization to a workplace mindfulness training (WMT) or a waitlist control condition on teachers’ well-being (moods and satisfaction at work and home), quantity of sleep, quality of sleep, and sleepiness during the day were examined in 2 randomized, waitlist controlled trials (RCTs). The combined sample of the 2 RCTs, conducted in Canada and the United States, included 113 elementary and secondary school teachers (89% female). Measures were collected at baseline, postprogram, and 3-month follow-up; teachers were randomly assigned to condition after baseline assessment. Results showed that teachers randomized to WMT reported less frequent bad moods at work and home, greater satisfaction at work and home, more sleep on weekday nights, better quality sleep, and decreased insomnia symptoms and daytime sleepiness. Training-related group differences in mindfulness and rumination on work at home at postprogram partially mediated the reductions in negative moods at home and increases in sleep quality at follow-up.