Aims: This study searches for developmental mechanisms explaining why parents possess less knowledge about their adolescent children, as these get older. Family processes related to adolescents’ striving for and parents’ granting of autonomy, and adolescents’ relations outside the family might be such developmental mechanisms.

Methods: A total of 2,415 Swedish adolescents aged 13 to 18 participated in at least two consecutive waves of a five-year time-sequential survey study with annual assessments. Of a sub-sample of 10-16 year-olds, 1,223 parents filled out questionnaires at Times 1 and/or 3. Multi-level analyses were conducted to test whether family process variables and adolescents’ relations outside the family explained intraindividual residual change of parental knowledge, and whether these effects explained normative age variations of knowledge.

Results: Adolescent-reported parental knowledge declined more and more steeply with age. Adolescents’ reduced disclosure of information and their defiance of parental requests explained about 40 percent of this normative age variation. Other processes such as increasing parental solicitation of information and adolescents’ improved peer relations had an enhancing effect on parental knowledge and thus slowed down the decline of knowledge. Few gender differences occurred.

Conclusions: Adolescents achieve autonomy from parents by managing information they provide to them and by acting against parental requests. These autonomy-related behaviors explain a large portion of the normative age decline of knowledge. However, increased parental solicitation and improved relations outside the family increasingly contribute to parental knowledge, thus limiting its decline. This suggests that family members balance adolescents’ autonomy and their connectedness with the family.