The smartest kid in the room might be the one who never raises a hand. Ask them directly sometimes.

Speaking up measures comfort with speaking up, which is not the same as understanding. Some people process before they talk, some grew up in rooms where interrupting was expensive, and some simply do not enjoy an audience. Their thinking is not less developed for being unspoken, only less available to everyone else.

Ask quietly rather than putting them on the spot. A direct question in a small moment, or a message afterward, gets you what a room never will. And if you are the one who stays quiet, a written answer counts every bit as much as a raised hand.