Look at this picture of a pattern-block triangle standing beside a mirror. The triangle points to the right. Its reflection sits in the mirror.

Which way is the reflection pointing? The same way as the triangle, or the opposite way? Have a good look before any hands go up.

The interactive reflects each shape across a mirror line. Watch which way the shape flips, and count the squares from the line to a corner and back the same distance on the other side.

Now we reflect four shapes together on the board, one at a time. Each shape is already on one side of the mirror line. We count how many squares each corner is from the line. Then one of us taps the squares where the reflection goes, on the other side of the line. We all check it, press Check, and Next brings the next shape.