A child points to a long four-sided shape and calls it a rectangle. Then they point to a square and say it cannot be a rectangle because it is not long. The drawings have taught a visual habit that the definitions do not support.
In the usual inclusive classification of plane shapes, a rectangle has four right angles. A square meets that condition and also has four equal sides. Every square is therefore a rectangle, although many rectangles are not squares.
Sort by a property you can check
Cut several paper quadrilaterals: squares of different sizes, non-square rectangles, and shapes with sloping corners. Keep the examples clearly drawn. Ask children to group the shapes with four right angles before introducing the group name.
Use the corner of a sheet of paper as a simple right-angle comparison. A ruler helps compare side lengths. Explain that a classroom measurement may be approximate; the mathematical shape is defined by its properties rather than the precision of the scissors.
Put one group inside another
Draw a large loop labelled rectangles. Inside it, draw a smaller loop labelled squares. Place every square in the smaller loop, which is also inside the rectangle group. Put the non-square rectangles in the remaining space within the larger loop.
Ask two questions separately: “Does this shape have four right angles?” and “Does it also have four equal sides?” The first establishes rectangle membership. The second identifies the square subgroup.
Rotate the examples
Turn a paper square so a corner points upward. Its side lengths and angles have not changed. Calling every tilted square a different kind of shape can obscure that fact. Invite the child to justify a classification by checking properties rather than pointing to the direction in which the shape sits.
Finish with a request to draw a rectangle that is not a square, then a rectangle that is a square. If the second instruction seems impossible, return to the nested groups. The useful learning is that a shape can belong to more than one category without either name being wrong.