Understand the idea.
Flat shapes and solid objects
A flat shape has no depth. A drawn circle describes a flat shape. A real ball is a solid object: it takes up space in more than just a flat surface.
A flat page can contain a picture of a solid object. When you see the block, ball and can pictures, think about the real objects they represent. Drawing a ball does not make the real ball flat.
Choose a rule
A sorting rule tells you which features to look for. To sort flat shapes by straight boundaries, trace each outline. Put a shape in that group only when every part of its boundary is straight.
Solid objects can be sorted by their surfaces. A block has flat surfaces; a ball is curved all around. Keep using the same rule for every item so you can explain why each belongs in its group.
See the method in action.
Sort a ball and a circle
Which is a solid object: a drawn circle or a real ball?
Worked solution
- 1
Think about the real ball.
It has depth and takes up space, so it is a solid object.
- 2
Think about the drawn circle.
The circle describes a flat shape rather than a solid ball.
- 3
Choose the solid object.
The ball is the solid object in this pair.
The ball.
Sort straight boundaries
Which pictured flat shapes have only straight sides?
Worked solution
- 1
Check shape A's boundary.
The triangle has only straight sides, so A fits the rule.
- 2
Check B and C.
The square and rectangle also have only straight sides, so both fit.
- 3
Check D and name the group.
D has a curved boundary, so leave it out. The straight-boundary group is A, B and C.
A, B and C.
Try it yourself.
Check your understanding
A cube-shaped block and a drawn square look related. Are both solid objects?
Show answer & reasoning
No. The block is solid; the square is a flat shape.
No. The cube-shaped block has depth and takes up space, so it is solid. The drawn square describes a flat shape.
Keep practising
6 worksheet questions
Read the questions online
- Sort these words into flat shapes and solid objects: triangle, ball, square, cube.
- Which pictured object is a cube-shaped block?
- Which pictured flat shape has a curved boundary?
- A child sorts a circle with triangles using the rule only straight sides. Does it belong?
- A can has flat round ends and a curved side. Must it be a ball?
- Choose a fair sorting rule for a square, triangle and circle. Show your groups.
Read the worked solutions
- Sort these words into flat shapes and solid objects: triangle, ball, square, cube.
Think about the named shape or object, not the printed words.
Flat: triangle, square. Solid: ball, cube. - Which pictured object is a cube-shaped block?
A shows flat square faces.
A. - Which pictured flat shape has a curved boundary?
It is a circle.
D. - A child sorts a circle with triangles using the rule only straight sides. Does it belong?
The circle's boundary is curved.
No. - A can has flat round ends and a curved side. Must it be a ball?
A ball is curved all around; a can also has flat ends.
No. - Choose a fair sorting rule for a square, triangle and circle. Show your groups.
State one rule and apply it consistently.
Answers vary: for example, straight boundaries: square and triangle; curved boundary: circle.
Curriculum reference & lesson scope
Australian Curriculum v9 / SA Curriculum 2026
Year 1 making, sorting and describing familiar shapes and objects using spatial features.
Official curriculum source ↗