Back to school for Pennsylvania Ballet

‘Don’t be nervous,” Pennsylvania Ballet artistic director Roy Kaiser told the 23 girls and two boys with their left hands on the barre, wearing solemn expressions and numbers pinned to their neat dance clothes. “Relax and work hard.” The first of two groups of 12- to 14-year-olds followed principal dancer Arantxa Ochoa through an hour of pliés, tendus, jetés, and pirouettes last Sunday morning in the company’s East Falls studios.