Michael Schoch, Answers questions on Noodle
I don't know if Sabish Middle School offers dance classes, but Fond du Lac High School has a dance team. Similarly, the theater program and P.E classes seem to offer some dance-related activities. To get the most accurate answer possible, I recommend calling the middle school at (920) 929-2800.
Using the Noodle search engine, I found a number of dance studios and tutors near Fond du Lac. If the middle school doesn't offer classes, maybe one of these other facilities will have what you need.
Best of luck and feel free to write back any time!