A line plot puts measurements on a number line and stacks an X above each one. The gap is as much of the picture as the marks are — free printable sheets, with an answer key.
If they get stuck
The answer key prints on a separate page.
The scale of the ruler is the difficulty. Whole inches is the grade 2 plot; halves and fourths are the grade 3 one, and the picture is otherwise the same — which is exactly why it is the one control these sheets offer. Eighths are there too, for a class that has met them.
Every plot on these sheets has at least one empty position, and most of them are marked. That is not decoration: a length nobody measured is a fact about the data, and a plot with no gaps is a bar chart with thin bars. Every question answers with a count or with a position on the plot's own ruler, so the sheet can be marked without asking a child to add fractions in a blank.
Height of the bean plants (inches)