The acculturation process is an important part of the experience that immigrant children and their families go through when adapting to live in a new country. Most studies on acculturation have included immigrant groups – mainly adults – living in North America and Europe. This thesis seeks to redress that imbalance by focussing on the acculturation attitudes and well-being of children and adolescents both in Chile and the United Kingdom (UK). A further important aspect is to examine how the discrepancies in acculturation within the family relate to children's well-being and family relationships. In this thesis, a bi-dimensional approach (both desire for culture maintenance and culture adoption/desire for contact with other groups) is used to test various hypotheses about the relationship between acculturation orientations - children's, parents' and discrepancies between the children and parents - and well-being of children. Several features characterise the research: two different receiving contexts (UK and Chile); different national origins of participants (with immigrant background and non-immigrant background); use of cross-sectional, longitudinal and qualitative methods; use of both perceived parent and actual parent scores; and the presence of social mediators and moderators (e.g., perceived discrimination, perceived peer acceptance, perceived school climate and perceived family relationship). The main findings were that, both in UK and Chile, immigrant children showed preference for maintenance of their heritage culture (CM) and establishing contact with receiving groups (DC) (or adopting the receiving culture (CA)), and that this preference was related to better well-being than other options, both concurrently and longitudinally. The acculturation discrepancies between children and parents had different consequences on well-being if they were on CM, CA or DC, depending on the measure used to calculate the discrepancies and also for immigrant and non-immigrant children. The findings are discussed in relation to the existing literature, and implications are drawn for improving psychological adjustment of immigrants and for future research that is needed.