Roll out half the pastry and line a 9-inch pie pan; trim crust to the rim of the pan. Loosely cover with plastic wrap and refrigerate.
Combine sugar, tapioca, and cinnamon. Toss sugar mixture with blueberries in a mixing bowl and sprinkle with lemon juice. Let stand fifteen minutes.
Meanwhile, roll out the top crust into a 10-inch circle. Cut into half-inch strips. Pour blueberry mixture into chilled pie shell and dot with butter. Add the pastry strips one at a time, weaving a lattice. Flute edges.
Place pie on a baking sheet to catch drips.
Bake in the preheated oven for 40 to 50 minutes, until filling is bubbly and crust is light brown. Cool completely before serving.
Frost is a common problem with wild blueberries and is the primary cause of a poor harvest. Not all blueberry farms have the same climate. The fields in Quebec and Maine blossom before the fields on Prince Edward Island and are therefore more susceptible to frost. The later blossoming of Island berries usually occurs after the last frost of the spring.