A panel for a drop ceiling is made of a semi-rigid but resilient material such as spring steel and includes corner clips adapted to cooperate with the inverted T-shaped stringers of a drop ceiling support system so that the panel is self-centering between opposing stringers and is spring biased into a clamped relationship with horizontal flanges of the inverted T-shape stringers to prevent the panel from moving up and down. The corner clips are also designed to transfer any horizontal compressive shear force in the mounting system to vertical edges of the panel so as not to undesirably bow the flat base of the panel.