The teenage years can be mystifying for parents. Sensible children turn scatter-brained or start having wild mood swings. Formerly level-headed adolescents ride in cars with dangerous drivers or take other foolish risks.

A flood of new research offers explanations for some of these mysteries. Brain imaging adds another kind of data that can help test hypotheses and corroborate teens’ own accounts of their behavior and emotions. Dozens of recent multiyear studies have traced adolescent development through time, rather than comparing sets of adolescents at a single point.

The new longitudinal research is changing scientists’ views on the role parents play in helping children navigate a volatile decade. Once seen as a time for parents to step back, adolescence is increasingly viewed as an opportunity to stay tuned in and emotionally connected. The research makes it possible to identify four important phases in the development of intellectual, social and emotional skills that most teens will experience at certain ages. Here is a guide to the latest findings:

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Ages 11 to 12

As puberty takes center stage, tweens can actually slip backward in some basic skills. Spatial learning and certain kinds of reasoning may decline at this stage, studies show. Parts of the brain responsible for prospective memory, or remembering what you are supposed to do in the future, are still maturing. This may be why a teen may seem clueless if asked to give the teacher a note before school.

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