Christoph Selter, Addition and Subtraction of Three-Digit Numbers: German Elementary Children's Success, Methods and Strategies, Educational Studies in Mathematics, Vol. 47, No. 2 (2001), pp. 145-173 ...

The answer will look like this. We can also use numbers instead of counters. This model shows 6 + 3 = 9. You can also use part-whole models to help with addition problems involving bigger numbers.

Primary Resources > KS1 Maths A fun series, featuring presenter Rodd, who uses rhymes and songs to help children with counting numbers, addition and subtraction.

Korean children's ability to solve addition problems with sums of 10, single-digit addition problems with sums between 10 and 18, and single-digit subtraction problems with minuends between 10 and 18 ...