I have a tile design on the grid. It was built by flipping and sliding one small shape, and it has a mirror line down the middle.

Which moves do you think made it: flips, slides, or turns? And where on the grid do you think each piece sits?

Two boards, and they belong together.

First, a symmetrical design. Each shaded square on the left has a matching square the same distance on the other side of the mirror line. Symmetry tells you where the partner square is.

Now three points on the co-ordinate grid. We read each one across first, then up, and write it as (across, up). A grid reference is how you name a square.

Key point Today we need both at once. To flip a point across a mirror line you have to find where it lands, and then say its name so somebody else can find it too.

Here is point A on the grid. This step is about the mirror line itself.

First say A's grid reference out loud, across first, then up. Then find where a vertical mirror line could sit. Count how many squares A is from the line you choose, because that is the same number of squares it will land on the other side.

Nobody is marked here. A pupil says the reference and the rest of the class agrees or corrects it out loud before we move on.

Our mirror line is the vertical line at 5 across, and you can see it on the grid.

How a reflection works. Count the squares from the point to the mirror line. Count that same number of squares past the line on the other side. That is where the point lands. The up number never changes in a vertical mirror, only the across number does.

We do these one at a time. Say the new reference aloud, across first, before the pupil at the board taps it in, and the class agrees before we start the next one:

1. Reflect (2, 3) across the mirror line at 5 across.
2. Slide (5, 1) three across and two up.
3. Reflect (7, 4) across the mirror line and read its new reference.