What Shapes Are the Same and Different?

Before children can sort, count, or classify shapes, they need to be able to look at two shapes and decide: are these the same, or are they different? This simple skill of comparing shapes is one of the very first steps in learning geometry. It teaches children to look closely at what makes a shape a shape, instead of just guessing by how it looks at a glance.

Two shapes are the same when they share the same important features, even if they are not drawn exactly alike. The features we check are:

• Number of sides: a triangle always has 3 sides, a square always has 4 sides.
• Number of corners: a corner is the point where two sides meet.
• Overall shape: is it round, or does it have straight sides?

A big red triangle and a small blue triangle are still the same kind of shape, because they both have 3 sides and 3 corners. Size and color can be different while the shape stays the same.

Shapes are different when they do not share those same key features. A square and a triangle are different because a square has 4 sides and 4 corners, while a triangle has only 3 sides and 3 corners. A circle is different from both because it has no straight sides and no corners at all.

When deciding if two shapes are the same or different, follow these steps in order:

• Step 1: Count the sides on the first shape.
• Step 2: Count the sides on the second shape. Do the numbers match?
• Step 3: Count the corners on each shape. Do the numbers match?
• Step 4: If both the sides and corners match, the shapes are the same type. If either number is different, the shapes are different.

Color and size are not part of this check. A tiny green square and a huge purple square both pass the test with 4 sides and 4 corners, so they are still the same shape.

Look at three shapes: a yellow square, a purple square that is much smaller, and a red triangle. The yellow square and the purple square are the same, because both have 4 sides and 4 corners, even though their size and color are different. The red triangle is different from both squares, because it only has 3 sides and 3 corners.

Once children can tell which shapes are the same and which are different, they are ready to group shapes into sets. This is exactly the skill used when children classify and sort by shape, and it also connects with learning to classify shapes by color as an extra way to compare. Later on, these same comparing skills help children place shapes into groups using a Venn diagram to show what shapes have in common.

Related lessons

• Kindergarten