Preheat oven to 375°F. Set a rack to the middle position.
In a medium-size bowl, whisk together flour, brown sugar, baking powder, baking soda, and salt. With a pastry cutter or 2 knives, cut butter into flour mixture until mixture resembles coarse crumbs. Stir in oats and raisins. Add buttermilk and mix with a fork until dough begins to hold together.
Turn dough out on a lightly floured surface and knead 6–8 times. Pat dough into a ½-inch-thick disk. Cut disk into 8–10 rounds or wedges and place on an ungreased cookie sheet. Do not separate.
Sprinkle with cinnamon and sugar. Bake until golden brown, 20–25 minutes.