A number line from 0 to 1000 allows students to locate, order, and reason about three-digit numbers. Benchmark numbers — 100, 200, 300, … 1000 — divide the line into equal intervals. A number like 450 sits halfway between 400 and 500. Using a number line to place and compare numbers builds a mental model of the number system that supports estimation and rounding.
Provide open number lines (endpoints only) and ask students to place specific numbers, justifying their placement. Work with scaled number lines where major marks represent 100 and minor marks represent 10. Connect to comparing: numbers farther right are greater.
You have already used a number line that goes from 0 to 20 — you know that numbers to the right are greater, numbers to the left are smaller, and the spaces between marks are equal. The number line to 1000 works in exactly the same way. The difference is scale: instead of moving one tick at a time, you move by hundreds. Your knowledge of place value (hundreds, tens, ones) becomes the key for navigating this much larger number line.
Benchmark numbers — 0, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000 — act as anchors. They divide the number line into ten equal sections, just like 0, 2, 4, 6, 8, 10 divide a 0–10 line into five sections. Your prior work with skip-counting by 100s means you already know these landmarks by heart. When you want to place 650, you first locate 600 and 700, then find the halfway point (650), and place the number there. When you want to place 720, you know it is closer to 700 than to 800 — 20 out of 100 of the way from 700 toward 800.
The reason place value matters so much here is that the digits tell you exactly where to look. The hundreds digit tells you which section of the number line you are in (6__ means between 600 and 700). The tens digit tells you how far into that section (65_ means 50% of the way from 600 to 700). The ones digit makes fine adjustments. This is place value turned into a spatial location — a number is not just a count, it is a position.
Placing numbers on this number line is preparation for rounding, which you will use soon. Rounding asks: is this number closer to the lower hundred or the upper hundred? If you can picture 650 sitting exactly in the middle between 600 and 700, you already understand the hardest part of rounding to the nearest hundred. The number line makes "closer to" a visual, intuitive question before it becomes a rule.