Once students have gained an understanding of addition and subtraction (See "What to do when you can't Add & Subtract"), then they can gain more skills using the strategies for multiplying and dividing numbers.
These highly accessible books are written for parents, older pupils, students and adults and offer a non-patronising, consistent and developing pathway through basic arithmetic.
Author Steve Chinn is one of the foremost authorities on dyscalculia with 24 years experience as Head of three schools for dyslexic pupils, plus many years experience teaching in mainstream schools.