We bought some of those drill and kill Kumon books. Frankly, I do think they have helped alot in terms of improving speed and accuracy and well as not writing numbers the wrong way, etc. Repetition really helps.
Actually, my fourth grader just got all 15 of 15 math questions right on his one-minute speed test! (I don't know if it was multiplication or what). He had at age 6 on the WISC on 99th percentile on most parts and a 43rd percentile on PSI.