Grid Algebra is available from the Association of Teachers of Mathematics and there is support on their website. I have successfully used this with two Y9 classes of differing abilities. With one group we practised multiplication and division tables, the others we built expressions. In both classes it was evident that I was doing much more questioning than would have been possible through exercises, and more formal teaching. The students commented on the fact that it was helping them to think about what they were doing and how the table was structured.