Although I found these awhile ago and used them with my non-LD daughter, I recently pulled them out and started using them with my LD son and I really like them:
Made by Key Curriculum Press they have “Key to Fractions,” “Key to Percents,” “Key to Decimals,” and they also have key to Algebra, Geometry, Measurement and Metric Measurement. Each has a series of little workbooks that are relatively inexpensive (I paid about $3 for each) and there’s an answer book as well.
I found them at a local educational supplies store (I think most general educational stores carry this series). What I like is they start out very simple and slowly build on concepts. My son seems to have an easy time going through them and they are helping reinforce the concepts he’s learning at school.
I don’t mean to sound like an advertisement, and I don’t work for this company, but I do like their workbooks and figure someone else may find them useful too.