Subitise what's next based on the structure of ten. Support students to talk about tens and ones within a number made or as they make the number. To see how large numbers are and compare. Estimate how many piled on the floor and rounding 

They support a more structured use of adding and subtracting  with 2 digit numbers, building to next ten or over the next ten, partitioning of numbers,  

1 more / 1 less, 10 more/ 10 less

If used with smaller strings can support ten facts and facts to 20. Guessing what’s missing when some of the ten are covered,

They can also be used to show groups when multiplying and enable students to divide a given amount.

Strings of 100 are perfect for percentages, negative numbers. 

Which students attempt to use them when asked to make 2 digit numbers?

When used what supports to you also offer to use structure – ten frames double frames, rather than disorganised mess we often see.

But can be deconstructed as student explore how to rename

At some point they need to be very concrete, able to picked up, pulled apart or manipulated. The use of materials can build in from the outset that mathematics is fundamentally an experimental science, conjectures need to be made and evaluated in place of simply acquiring a mass of seemingly immutable facts and rules.