--- - |2 The purpose of this research was to analyze the development of self‐concept during adolescence. Participants included 484 teenagers (226 boys and 258 girls) from middle‐class families in the Basque Country region of Spain (Mage = 14.99, SD = 1.81 in Time 1 and Mage = 15.64, SD = 1.80 in Time 2). Longitudinal analysis found differences in the general school dimension. Six dimensions (math, verbal, general school, physical abilities, parent relationships and same‐sex relationships) reported a linear trend with a decreasing monotonic pattern; self‐esteem fit a cubic trend and physical appearance a quadratic trend line. Males showed higher means in self‐esteem, math, physical abilities, physical appearance, emotional stability and parent relationships; and females had higher values in verbal and general school. - Journal of Research on Adolescence, EarlyView.