Whilst less efficient than the traditional method, grid multiplication is considered to be more reliable, in that children are less likely to make mistakes.
Faced with a slightly larger multiplication, such as 34 × 13, pupils may initially be encouraged to also break this into tens.
So, expanding 34 as 10 + 10 + 10 + 4 and 13 as 10 + 3, the product 34 × 13 might be represented: Totalling the contents of each row, it is apparent that the final result of the calculation is (100 + 100 + 100 + 40) + (30 + 30 + 30 + 12) = 340 + 102 = 442.
Once pupils have become comfortable with the idea of splitting the whole product into contributions from separate boxes, it is a natural step to group the tens together, so that the calculation 34 × 13 becomes giving the addition so 34 × 13 = 442.
However, by this stage (at least in standard current UK teaching practice) pupils may be starting to be encouraged to set out such a calculation using the traditional long multiplication form without having to draw up a grid.
For example, the calculation 21/2 × 11/2 can be set out using the grid method to find that the resulting product is 2 + 1/2 + 1 + 1/4 = 33/4 The grid method can also be used to illustrate the multiplying out of a product of binomials, such as (a + 3)(b + 2), a standard topic in elementary algebra (although one not usually met until secondary school): Thus (a + 3)(b + 2) = ab + 3b + 2a + 6.
On platforms that support these instructions, a slightly modified version of the grid method is used.