A ceiling system in one embodiment includes a support grid including intersecting grid support members and grid openings formed between the grid support members. A vertical baffle is positioned in a grid opening and is attached to the support grid. The baffle includes opposing front and rear faces extending between opposing lateral sides of the baffle. First and second mounting grooves formed in the baffle engage and support the baffle from the grid. In one embodiment, one of the mounting grooves is disposed in each lateral side to support the baffle from opposite sides. The baffle may further include a third mounting groove formed in the rear face which engages the support grid to help align and squarely register the baffle with respect to the grid for clean linear visuals. In one embodiment, the grid support members may have a standard T-shaped cross section.