According to Official Guinness Records,
The largest ballet lesson consisted of 1,530 people, achieved by Yan OI Tong and DNA WeCheck Limited (both Hong Kong) at KITEC in Kowloon, Hong Kong, China on 3 February 2018. The participants consisted of ballet students ranging in age from primary school to high school. School teachers were also present in each section, demoing the movements.
For a complete list of 2018 records, please visit 2018 Guinness Records in China.