Happiness, or subjective well-being, the self-evaluation of how happy or unhappy a person is, has been studied amongst adults using a variety of self-report methods. However, there has been relatively little related work with children. A psychometrically valid and reliable SWB measure for schoolchildren aged 8- to 15-years-old, the School Children's Happiness Inventory (SCHI), was piloted and developed against existing measures of self-esteem, affect and depression (n = 71). Predictive validity (n = 771) was assessed using a measure of being bullied, sharing the same context (school) and time scale (the previous week). The School Children's Happiness Inventory (SCHI) may be especially useful in assessing the effect of school-based interventions and influences on schoolchildren's well-being. SCHI Measure, Instructions and Norms are appended. (Contains 7 tables and 3 figures.)