While about 20 first-graders sat on the floor in a classroom at Plymouth River Elementary School in Hingham, teacher Sue McHugh drew on the white board and stepped away.

“What’s the name of this shape, everybody?” McHugh asked.

“Square,” the kids answered.

Next, McHugh drew a rectangle.

“Put your thumb at your heart if you notice a difference in those two shapes,” McHugh said. Most of the kids did.

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