What are open number lines?
An open number line starts as a line with no numbers. They can be used as a visual representation for recording thinking during the process of mental computation.
Why are open number lines so useful?
Open number lines are a great tool to get students to move past manipulatives to representing their thinking on paper. Using this strategy will increase students’ confidence in their ability to use numbers flexibly which will lead to stronger number sense. Using them will also help students who are not ready for the algorithm yet, but will shrink the gap because of the number sense it builds. Open number lines can be used by students to represent their thinking with many different concepts, including addition, subtraction, multiplication, division, and elapsed time. Open number lines are less time consuming than waiting for students to record all the numbers on a 0-100 ranged number line. It is also useful that the space between lines do not need to be precise on an open number line. It’s truly about using a tool to help you understand and think through a problem.
How do I get students to use open number lines?
To expose students to open number lines, it is great to start with a pre-made concrete example that they can explore and discuss. It is also helpful to use questioning to encourage a student to try the strategy while the class is problem solving. Have that student share their open number line with the class. It always works best if the teacher is very excited about this new strategy and records the example on an anchor chart. Challenge all students to use an open number line when working on their next problem(s).
What resources are available?
Open number lines can be drawn on white boards and in math journals. There are also resources available that could be cut and laminated for students to use, including this one.
This video has students demonstrating how to use an open number line. For more information on open number lines, Marilyn Burns explains how she uses them when subtracting with students on her blog.
There is also an Open Number Line Mini PDM located in the Mini PDM folder on our IDEAS Elementary Math Bulletin board.