A general conception of subjective well-being considers at least one cognitive dimension, normally linked to life satisfaction, whether measured as global life satisfaction or satisfaction with specific areas of life, as well as considering an affective dimension normally evaluated through the presence of positive and negative emotions or affective balance. This chapter will address the differences between boys and girls both in childhood and in their transition to adolescence, and the changes that occur at this stage of the life cycle in relation to subjective well-being. It will address the existing evidence of the change in self-reported levels of satisfaction at this stage and the differences seen between boys and girls, both phenomena being widely addressed in contemporary research and on which there is some agreement about their occurrence. However, various explanations coexist that do not account for the phenomenon at a multicultural level. Evidence will be presented based on the accumulated evidence of the ISCWeB study (The International Survey of Children’s Well-Being) which has a sample of more than 30,000 children and adolescents from more than 30 countries.