Separation-individuation is one of life’s most difficult passages: it is completed successfully by most; however, more than might be suspected remain in the mire of adolescence all their lives. Prepubescence is supposed to erupt in adulthood – adults emerging where clingy parent-dependent pre-teens once held sway. It is a passage equally traumatic to boys as it is to girls, but in “Dance Nation” currently running at Playwrights Horizons’ Peter Jay Sharp Theater, playwright Clare Barron chooses to focus on this process from the point of view of “pre-pubescent” girls. The trope chosen to immerse the audience in this time of trauma is the extended metaphor of the dance studio.