In addition to the Murderous Maths, you may want to consider the Life of Fred Series. Although we haven't used them (yet), I've peeked at my niece's books and they seem great! Other users on this forum can give you more first hand knowledge.


http://www.stanleyschmidt.com/FredGauss/index2.html
From their website:


1) When should my child start the series?

Life of Fred: Fractions is the first book in the series. It presupposes that the reader knows three things:
i) the addition tables What's 5 + 8?
ii) the multiplication tables What's 7 times 8?
iii) long division What's 6231 divided by 93?

Mom to DYS-DS6 & DS3