What do people mean when they talk about strings in math?

A number string is a set of related questions that build on each other from simpler to more complex and highlight number relationships.

For example, at the K–2 level, a string like the one below highlights the fact that if you add the next consecutive number to itself (which is, of course, doubling it), you add 2 and the only results you get are even.

1 + 1 = 2
2 + 2 = …
3 + 3 = …
4 + 4 = …
…

At the Grade 3–5 level, a string like the one below highlights the fact that if you have four groups and increase the group size by 1, the total increases by 4.

4 × 4 = 16
4 × 5 = …
4 × 6 = …
4 × 7 = …
…

At the Grade 6–8 level, a string like the one below highlights the fact that if you divide a factor by 10, you also divide the quotient by 10. It also highlights the consistency of digits wherever the decimal point might be.

3 × 1428 = 4284
3 × 142.8 = …
3 × 14.28 = …
3 × 1.428 = …
…