At the beginning of Year 1 children will practice placing numbers on a number track and then the language of one more and one less will be introduced. They need to know that one more is the number after the starting number and one less is the number before and should use their counting skills to help. By the summer term they will be able to do this with numbers up to 100.
Finding ten more and ten less than a starter number can be introduced much later in the year for those children who have an understanding of what each digit represents when partitioning a 2-digit number and can count happily in steps of 10. We have just published a further set of resources looking at finding ten more or ten less than a given number.