Supporting student wellbeing in schools is increasingly becoming a global priority. However, research and initiatives primarily focus on general wellbeing rather than subject-specific experiences. Given the pervasive levels of mathematics anxiety, negative attitudes, and disengagement in mathematics education, we argue for a more contextualised wellbeing approach. We define 'mathematical wellbeing' (MWB) as the fulfilment of values whilst learning mathematics accompanied by positive feelings (e.g., enjoyment) and functioning (e.g., engagement) in the discipline. We report on 3073 New Zealand Year Three to Eight students' responses to a survey measuring their fulfilment of seven MWB values: accomplishments, cognitions, engagement, meaning, perseverance, positive emotions, and relationships. Students' MWB was highest for relationships and perseverance and lowest for engagement and positive emotions; MWB declined from Years Three to Eight; females often rated higher MWB than males; school sociodemographic status was mostly not significant, whilst engagement and positive emotions differed across ethnicities. Research implications include understanding target areas to improve diverse students' experiences and wellbeing in mathematics education.