Youth Dance Ensemble at Joy of Motion is a serious dance company with excellent training. Ballet is part of the training but most of the dances performed are modern, with some jazz. I would recommend starting when your DD is old enough for Level 2, which I think is age 10/grade 4.

Excellent training in musical theatre, jazz, tap, modern and voice.
Also, performing company for her age.
Just over the dc line past Sibley Hospital, off MacArthur Blvd.
youthperformingartsschool.com

thanks, PP! forgot to mention we are in DC, so this was helpful. Anyone else?

Joy of Motion and Jones Haywood.
http://www.joneshaywood.com/

My almost 9-year old DD really wants to take more dance classes (not ballet). What, in your opinion, are the best and most intense classes offered for kids her age? She is amazingly strong and athletic, and more important, super-serious with focus and concentration. Recommendations? We tried Dance Institute of Washington but were seriously underwhelmed with the organization, communication, and quality of her class---but willing to try again in case we had an atypical experience. Thanks in advance for your recommendations!