ACARA v9 CONTENT DESCRIPTION “create symmetrical patterns, pictures and shapes with and without digital tools, and describe translations, reflections and rotations of shapes”
The previous unit found lines of symmetry inside a shape; this one uses the same idea to move shapes around. A reflection flips a shape across a line, making a mirror image on the other side, the same distance from the line as the original. Every point of the shape has a partner point exactly opposite it across the line. This is the fold made into a movement: where line symmetry asked whether the two halves of one shape match, reflection takes a whole shape and produces its mirror twin. It is the first of three movements this unit names.
Reflect across a line
Reflecting flips a shape over a line; the image is its mirror.
A shape sits beside a vertical line. Reflect it and the mirror image appears on the other side.
Building symmetry by reflecting
Reflection is the tool for creating symmetrical patterns. Start with half a pattern on one side of a line, reflect every shaded square to the matching position on the other side, and the whole becomes symmetrical. Each square finds a partner the same distance across the line, just as the halves of a symmetrical shape do. This is how symmetrical pictures, borders and tile designs are made — not by guessing, but by reflecting a half across a line. A child who can complete the mirror half understands symmetry as something they can build, not only spot.
Complete the pattern
Mirror the left half across the line to build a symmetrical pattern.
Half a pattern sits left of the dashed line. Add the mirror half to make it symmetrical.
Sliding without turning
The second movement is the translation, or slide: moving a shape in a straight line without turning or flipping it. A slid shape keeps the same size, the same way up and the same facing; only its position changes. Sliding is the simplest movement to picture — like pushing a book across a table — and it is the one that changes least about the shape. Recognising a slide means checking that nothing but position has changed: no mirror, no rotation, just a move along a straight path.
Slide it (translate)
A translation moves a shape without turning or flipping it.
A translation slides a shape in a straight line. It does not turn or flip.
Three ways to move a shape
There are three movements that keep a shape the same size: the slide (translation), the flip (reflection) and the turn (rotation). A slide changes only position; a flip makes a mirror image; a turn spins the shape around a point. Naming them apart is the Year 4 skill, and the test is to ask what changed. Same facing and just moved along? A slide. Mirrored across a line? A flip. Spun around? A turn. These three names describe every rigid movement a flat shape can make, and they appear everywhere from patterns to puzzles to screens.
Slide, flip or turn?
Each movement has a name: slide, flip or turn. Match the description.
Slide, flip or turn: a shape moved straight across, same way up?
Symmetry you can construct
Putting reflection to work, a symmetrical design can be built tile by tile: place a tile on one side of the line and its mirror partner appears on the other, so the design is symmetrical at every step. This is exactly how digital tools draw symmetrical art, and doing it by hand makes the rule plain — symmetry is kept whenever each part is matched across the line. Building this way, a child never has to check the finished design for symmetry, because it was symmetrical from the first tile, by construction.
Build a symmetric design
Place a tile on the left and its mirror appears on the right automatically.
Each tile you place on the left gets a mirror partner on the right, so the design stays symmetrical.
What stays the same
The three movements differ in what they change, but agree on what they keep: a slide changes position, a flip mirrors, a turn changes facing — yet none of them changes the size or shape. A shape and its slid, flipped or turned image are always identical in size, a property called congruence. This is the deep idea behind all three: they move a shape around the plane without distorting it. With reflection used to build symmetrical patterns, and slide, flip and turn named and told apart, a child can both create symmetry and describe how any shape has moved — the language of transformations that geometry builds on next.
What each movement changes
Slide, flip and turn each change something, but never the size of the shape.
Each movement changes something different. Reveal each row to compare.
Quick self-check
1. Reflecting a shape across a line makes...
2. To complete a symmetrical pattern from its left half, you...
3. Sliding a shape straight across, same way up, is called a...
4. A left footprint and a right footprint are related by a...
5. Which of slide, flip and turn changes the size of a shape?