Number strings, also called problem strings, refer to a related series of mental math problems that are designed to draw out student thinking, help students notice relationships and develop explicit reasoning strategies.  Here’s the basic idea in 62 seconds:

http://https://www.youtube.com/watch?v=BbwlXI-F8qY

Getting Started

This site has a bunch of prepared number strings for addition, subtraction, multiplication, division, rational numbers and algebra. Teachers can search for strings by topic and then look for specific strings that would support students to learn specific content within those topics.

The resources here (the link to the PowerPoint and the pdf – a Number String Planning Guide and two models) were developed by Michael Pershan and Kristen Grey and shared at the 2016 NYC Twitter Math Camp.