This from the public Twitter of My Ballet (which stands for Manhattan Youth Ballet):
"Alumni Joseph Harrington now Billy Elliot on Broadway taking class with Level 5, class taught tonight by Jacqueline Schiller."
According to their website, the academy's program is modeled after the great European schools of ballet wherein students (aged 8-17) progress through levels of training that are carefully designed to address their physical, technical and artistic development. Generally, students will spend two years at each level. At age 12, Joseph is at level 5, out of a total of 8 levels.
More information on the school:
http://www.manhattanyouthballet.org/