Gisela Adisa, Jessica Hendy, Eric Michael Krop, and others will also be on hand to sing new arrangements of the pop performer's hits.
Howard recently appeared in Roundabout Theatre Company's Violet as well as in the original Broadway cast of Matilda.
The two-time Tony nominee gets one of Broadway's highest honors.
Luff takes on the role of Miss Honey.
Four actresses who aren't even 10 will lead the musical at the Shubert Theatre.
Check out photos from the final lunchtime concert of the summer.
The musical comedy gets new life at the New York Performing Arts Library.
The show is a fill-in-the-blanks whodunit written by Billy Mitchell.