Numberlines are a great math model: Use in small guided math groups
The Math Common Core emphasizes the use of number lines to help students understand the math they are doing. See this site to have a close look at how that looks across the grade levels. Numberlines are underutilized across the grade levels. Start using them in Pre-k (by having the students walk a big numberline). In 1st and 2nd grade they should use big ones that they can walk and little ones that they can use to explore, model and discuss their thinking. In 3rd, 4th and 5th grades students can work on multiplication, division, fractions and elapsed time with numberlines.
Remember that numberlines are models for mathematical thinking. Whenever students are using models, they should be explaining their thinking as they work. Be sure to do some of this in Guided Math groups so that students can spend time discussing the mathematics. They should not only talk about how they are representing their thinking but what the math is behind the representation. All students should have time to talk with each other, ask questions and respond, and small guided math groups allow them this time.
Please be sure to let me know how it goes!