A box plot says five things about a set of numbers and nothing else, and knowing which five is most of what there is to learn. These free printable worksheets ask for each of them off a drawn diagram: the smallest, the quartiles, the median and the largest.
If they get stuck
The answer key prints on a separate page.
The five-number summary splits the data into four equal parts, so each section of the plot holds a quarter of the values however wide or narrow it looks. That is the thing to say out loud, because a long whisker looks like "most of them are up here" and means the exact opposite — the values there are spread out, not numerous.
The box itself is the middle half, and its width is the interquartile range. It is the most useful single number on the diagram and the one a child is least likely to reach for, since it has to be worked out rather than read.
One question from a sheet like this one, worked a step at a time — with a sentence saying what just happened and why.
Box plots, step by step