Sometimes even a champion needs a few pointers. “Do you see how Kendall brings the drama, Izzie?” Irish dance instructor John Lawrence Morgan said, one spring night in his Millersville dance studio.

With a mix of childlike enthusiasm and surprising maturity, 11-year-old Erin Mayo is moving up in the Irish dancing world. She’s got the trophies — and the blisters — to prove it. The Lewes sixth ...