Long multiplication: The final addition
The most obvious mistake in long multiplication is for a pupil to work out the multiplications correctly, but then forget to add these together to get the final answer.
Less obvious is when a pupil completes the calculation, but instead of adding in the final step, they multiply the digits together. So instead of 8 + 0 = 8 they work out 8 x 0 = 0 etc.
This miscalculation may be even more difficult to spot when a pupil multiplies by zero incorrectly . In this calculation, such a pupil has mistakenly calculated 8 x 0 = 8 and 3 x 0 = 3, so they seem to have correctly added. Looking at the tens column though lets us see that 6 and 4 have given an answer of 24, which means that they have been multiplied, not added.
Pupils need to understand that the two numbers are the result of multiplying separately by the units and the tens, and that they need to be combined to give a total, by adding.
Some pupils find it difficult to switch between multiplying and adding which is necessary in long multiplication. Providing a mix of simple addition/multiplication facts or mixing column addition with multiplying by a single digit, will help to increase their confidence and fluency.