Objectives: Teacher connectedness is an important factor for young people's well-being. The aim of this paper was to examine teacher connectedness in detail and its potential association with emotional wellbeing. More specifically, we set out to analyse whether teacher connectedness acted as a universal asset for boys and girls of different ages and countries as well as across adolescents with differing perceptions of their performance at school. Methods: The study sample consisted of 9,444 young people aged 11, 13 and 15 years who had taken part in the World Health Organization (WHO) collaborative survey Health Behaviour in School-aged Children in Spain and England. After examining differences in teacher connectedness associated with demographic factors, we used general linear models to analyse the relationship between teacher connectedness and emotional well-being (including interaction teacher connectedness by country) across different age and performance-derived groups. Results: Results indicated some significant differences in teacher connectedness associated with age, country and perceived performance, but a consistent positive association between teacher connectedness and emotional well-being regardless of demographic factors, country and perceptions of school performance. Older adolescents and low achievers reported lower level of connectedness to their teachers, but the association between teacher connectedness and emotional well-being operated irrespective of adolescents' age and perceived performance at school. Conclusion: Results support the perspective that teacher connectedness can act as a significant health asset that operates irrespective of key demographic factors, while they point to some inequalities in teacher connectedness associated with age and performance at school. These findings have significant implications for health promotion interventions.