What is a dunce cap and when was it used?

A dunce cap was a cone paper hat with a D on it. A dunce cap was used as punishment for slow children like getting a sum (arithmetic problem) incorrect. Children who wore a dunce cap was made to sit/stand in the corner (like a time-out). Today If you get an answer incorrect, no standing in the corner. Just staying at your desk. It's a good thing that big schools don't have dunce caps because if I went to school in the 19th century, I'll be ashamed.