To support understanding of the number system, it is useful to have a counting stick, a number line on the classroom wall and a 100-square. Pupils need to use simple structural apparatus of various types, in which collections of units can be combined into or represented by larger pieces. Bead strings are also helpful. Place value cards showing the place value of individual digits, and how two- and three-digit numbers can be partitioned into hundred, tens and ones, are essential.
At a later stage, a different type of structural apparatus provides a physical representation of units, tens, hundreds and thousands, or decimals. A place value chart can be used to build and partition larger numbers and decimals, while base-10 blocks provide a physical representation of these numbers.
Do we really make the most of our wonderful number system? includes discussion of how to use Base 10 apparatus to help develop understanding of decimals.
Manipulatives in the Primary Classroom is an NRich discussion paper that explores in depth issues relating to the use of structured apparatus.
See also Selecting and Using Resources for Learning