A church window is made of 16 pieces of glass. Every piece has two features - a shape (circle, triangle, square, diamond) and a number from 1 to 4.
In every row and in every column each shape must appear exactly once. And in every row and in every column each number must appear exactly once too.
A few pieces are already in place. Sometimes you only see the shape, sometimes only the number, sometimes both.
Look for the row or column that already holds three shapes. The fourth shape is then certain. The same works for the numbers.
You may hunt for shape and number separately. The shape often comes from the row and the number from the column - together they complete one piece of glass.
Example
For parents
What does this exercise practice?
The stained glass window practices logical reasoning along two axes at once. A mini sudoku has one feature, here two conditions interlock - the child has to keep both systems in mind and must not forget one over the other. Nothing is calculated; the numbers are pure labels, just like the shapes.
Common pitfalls
The most common mistake is to look only at the numbers and forget the shapes - or the other way round. A piece is only finished when both are right. And watch out for the diamond - it is taller than it is wide and is not the same as the square.
How to practice at home
Lay out four kinds of pasta or four kinds of buttons on a 4x4 paper grid so that each kind appears once in every line. Then add slips of paper with the numbers 1 to 4 - following the same rule. Whoever manages both at once has built a stained glass window.
Related: The Greater-Smaller Grid, The Picture Puzzle