An electric harp, flamenco dancing, and improvisation were on the programs when the Princeton Symphony Orchestra performed recently for hundreds of school children at Richardson Auditorium as part of the PSO Bravo School Day Concerts. Dancer Griset Damas-Roche and harpist Jacqueline Kerrod were the guest artists. PSO Music Director and Conductor Rossen Milanov encouraged students to let their fingers do some marching, taught students to waltz onstage, and looked for volunteers to time the orchestra’s performance of the “Flight of the Bumblebee.”