Can you teach schoolchildren to be kinder? We conducted a randomized controlled trial of Learn Kind—a kindness-based SEL curriculum for grades K-8, designed by kindness.org. Teachers—randomly assigned to either a treatment group, or a waitlist group—completed measures and questions (kindness grades, happiness, the Strengths and Difficulties Questionnaire, math and reading grades) reporting on approximately 1202 students at three time points (Time 1–Time 3). We found, first: from Time 1–2, the treatment group significantly improved on all measures ( \(\overline{\text{d} }\) = 0.38); the waitlist group did not significantly improve on any measure ( \(\overline{\text{d} }\) = 0.03); and the treatment group improved on all measures significantly more than the waitlist group ( \(\overline{\text{d} }\) = 0.34). Second, the improvements in the treatment group on all measures (except 'attention') persisted from Time 2–3 ( \(\overline{\text{d} }\) = 0.01); and on all measures the treatment group had improved Time 1–3 ( \(\overline{\text{d} }\) = 0.38). Third, from Time 2–3 the waitlist group improved significantly on happiness, emotions, and reading ( \(\overline{\text{d} }\) = 0.09), but improved significantly more than the treatment group only on emotions and attention ( \(\overline{\text{d} }\) = 0.08). Taken together, the study found that Learn Kind had a small positive effect on kindness, happiness, strengths and difficulties, and academic performance. The implications, limitations, and future directions of this research are discussed.
