NEW YORK (AP) — Students at a New York City public school working out to a Beyonce song got a big surprise when the superstar walked in and joined them.

About 85 students at P.S. 161 in Harlem were in the middle of a choreographed routine Tuesday to a song adapted from Beyonce's hit "Get Me Bodied" when the singer arrived.

The children were participating in a national simulcast of "Let's Move Flash Workout." It's part of first lady Michelle Obama's fitness campaign.

The singer joined in wearing stiletto heels and a T-shirt emblazoned with "Let's Move."

Thirteen-year-old Aisha Collier gushed "she's so beautiful." She told the New York Post she messed up a little when Beyonce first arrived but then got back into it and continued to dance and have fun.

Copyright (2011) Associated Press. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.