P4 Nets and Line Symmetry: Fold It and See

A flat cross of six card squares slides onto a green cutting mat. Anya has cut it out and joined the squares together. What will it fold into? The view tilts, the squares lift one by one, and the answer closes up in front of you.

That is Fold It Up, a 30-second Primary 4 episode of our Topic Explainers series. Watch it first, with or without sound (there is no voice-over), then read on. One move answers every question in it: fold it and see.

Fold It Up: a cross of 6 squares becomes a cube. Fold it up, fold it over, see it fit.

In the episode, the cross of six squares folds into a cube. A second shape, a column of five squares with a "foot" square beside the bottom one, also has six squares, but when it folds, two squares overlap and one side is left open, so it is not a net of a cube. Three more nets fold into a cuboid, a triangular prism and a square pyramid. Then the fold turns over instead of up: a house-shaped figure on a square grid is folded along a dashed line to see whether the halves match, and half of it is completed square by square.

Nets and line symmetry sit together in Primary 4 geometry. Under the 2026 MOE syllabus, nets are taught in P4 (they used to be a P6 topic), so many parents are meeting this with their child for the first time.

The method

Both topics in the video come down to the same habit: picture the fold before you decide.

Nets fold up. A net is a flat shape that folds up into a solid with no gaps and no overlaps. Every face of the solid appears exactly once in the net. In Primary 4, your child learns to:

identify the net of a cube, a cuboid, a prism and a pyramid,
name the solid a given net will make, and
recognise flat drawings of solids, where the edges you cannot see are drawn as dashed lines.

Figures fold over. A line of symmetry is a fold line that makes one half of a figure land exactly on the other half. In Primary 4, your child learns to:

tell whether a figure is symmetric,
decide whether a given straight line is a line of symmetry, and
complete a symmetric figure on a square grid when half of it and the line are given.

The questions to ask are the same each time. For a net: "If I fold this up, where does each square go? Does any face appear twice? Is any face missing?" For a line: "If I fold along this line, does every square land on a square?"

Worked examples

Worked example 1: is it a net of a cube?

The episode shows two shapes, each made of 6 squares.

Shape A is a cross: a column of 4 squares with one extra square on each side of the second square.

Shape B is a column of 5 squares, with a sixth square (the foot) beside the bottom one.

Step 1: Count the squares. Both have 6. A cube has 6 square faces, so both pass the first test. That is exactly why counting alone is not enough.

Step 2: Choose a base. Pick one square to stay flat on the table. For the cross, choose the square with four neighbours. It becomes the bottom of the cube.

Step 3: Fold the neighbours up. The squares on the left and right fold up to become the left and right sides. The square above folds up to become the back, and the square below becomes the front. The last square, at the end of the column, is joined to the front, so it folds over the top as the lid. Every face is used once: bottom, back, left, right, front and top. Shape A is a net of a cube.

Step 4: Try the same with Shape B. Choose the fourth square of the column as the base. The square below it folds up as the front, and the square above it folds up as the back. The next square up becomes the top. Now there is still one square left at the top of the column, and it comes down over the front, landing on a face that is already covered. The foot folds up as the right side. Two squares overlap on the front, and the left side is left open. Shape B is not a net of a cube.

A quick rule of thumb follows from Shape B: a net of a cube never has 5 squares in a straight line. Fold four squares in a row around the cube and you are back where you started; the fifth always lands on top of the first. A cube net also never has a 2 by 2 block of four squares, because those four cannot all fold to different faces. There are 11 different nets of a cube altogether, and finding a few of them is a lovely challenge.

Worked example 2: which solid will it make?

The episode folds three more nets. The fastest way to name the solid is to count the faces and look at their shapes.

The net has	Number of faces	It folds into
6 rectangles, in 3 matching pairs	6	a cuboid
2 triangles and 3 rectangles	5	a triangular prism
1 square and 4 triangles	5	a square pyramid

The cuboid in the video has a length of 3 units, a width of 2 units and a height of 1 unit, so its net has two 3 by 2, two 3 by 1 and two 2 by 1 rectangles: opposite faces match.

The prism and the pyramid both have 5 faces, so the shapes decide it. A prism has two matching ends (here, triangles) joined by rectangles. A pyramid has one base (here, a square) with triangles that all meet at one point at the top.

After folding, the video draws each solid the way a textbook does: the edges facing you are solid lines, and the edges hidden at the back are dashed. When your child sees a dashed line on a drawing of a solid, it means "this edge is there, but you are looking through to it".

Worked example 3: test a fold line, then complete the figure

The house figure in the episode is made of 14 squares on a square grid, in four rows. From the top:

Row 1: 2 squares in the middle (the roof)
Row 2: 6 squares across (the eaves)
Row 3: 4 squares
Row 4: 2 squares, one under each end of row 3 (the legs)

Step 1: Test the horizontal line. Fold the top half down over the bottom half. The two roof squares land on empty squares, because the legs underneath are at the ends, not in the middle. The halves do not match, so the horizontal line is not a line of symmetry.

Step 2: Test the vertical line. Fold the left half over the right half. Every square lands on a square. The halves match, so the vertical line is a line of symmetry.

Step 3: Complete the figure. Now suppose only the left half is drawn, with the vertical line beside it (the line is shown as a bar):

. . ■ | . . .
■ ■ ■ | . . .
. ■ ■ | . . .
. ■ . | . . .

Copy each square across the line, in the same row and the same distance from the line. The square at the far left of row 2 is 3 squares from the line, so its partner goes 3 squares to the right of the line, also in row 2. Do this for all 7 squares and the house is complete:

. . ■ | ■ . .
■ ■ ■ | ■ ■ ■
. ■ ■ | ■ ■ .
. ■ . | . ■ .

Count to check: 7 squares on the left and 7 on the right make 14.

Common mistakes

"It has 6 squares, so it must be a cube net." Shape B shows why not. Six squares is necessary but not enough; the squares must fold to six different faces.
Guessing instead of folding. Many children decide by how a net looks. Ask your child to point to one square and say which face it becomes, then the next.
Mixing up prisms and pyramids. Both can have 5 faces. Ask, "Are there two matching ends, or one base with a point on top?"
Sliding instead of flipping. When completing a symmetric figure, a common slip is to copy the left half across as it is, shifting it over. That gives a repeat, not a reflection. The square nearest the line on the left must be nearest the line on the right, and the farthest stays farthest.

Parent tips

You do not need special equipment. Squared paper, scissors and a few empty boxes are enough.

Flatten a box. Carefully open out an empty cereal box or tissue box. What you get is a net of a cuboid (with some extra flaps for glue). Ask your child to point to the pairs of matching rectangles, then fold it back up.
Hunt for cube nets. Draw six-square shapes on squared paper, cut them out, and sort them into "cube" and "not a cube" by folding. See how many of the 11 cube nets your family can find.
Predict, then fold. Before cutting, ask your child to colour the square that will become the lid. Folding shows whether they were right.
Fold-and-cut symmetry. Fold a sheet of paper in half, cut a shape from the folded edge, and open it out. The fold is the line of symmetry. Then try drawing half a figure on squared paper for your child to complete.

Keep it short and hands-on, and let your child do the folding. When they are unsure, ask "Which face does this square become?" rather than giving the answer. For a fuller picture of what moved in the new syllabus, our guide to the MOE 2026 syllabus changes explains why nets now sit in P4, and Primary 4 sample questions explained walks through the shape of a P4 paper.

Practising nets the way school teaches them

The end of the episode opens a card leaflet on two topic chips, Symmetry (P4) and Nets of Solids (P4). That is how the topics appear in Singapore Math Drills. Our Primary questions map to the Singapore MOE Primary Mathematics syllabus, including the 2026 placements, so nets sit in P4 for us too, beside line symmetry.

And practice stays calm by design: no guilt-tripping over a missed day and no dark patterns, with your child's progress only ever measured against their own. Fold it up. Fold it over. See it fit.

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