Gifted Issues Discussion homepage Forums Recommended Resources Looking for math worksheet

I am looking for help in finding math worksheets, or workbooks for DS6, he LOVES math. He just finished the Singapore workbook 3B, and we purchased 4A, 4B, and challenging word problems 4. He is home on break and did all of 3B in 3 days, not normal for him, 3A took him 5 months. I don�t set the pace, he does, this is just fun work outside of school. He understands the mechanics of the math very quickly, I am looking for problems that require more thinking, less (Plug and go). I am not very good at math, but much of the work has little problem solving. The Challenging word problems look somewhat better. If anyone else has another book or some other suggestions please let me know. The 4th grade stuff, although a little new is mostly an expansion on third grade with some percentage work thrown in. I am a novice at this, and am somewhat uncertain as to how to keep it new and fun, yet hard enough to keep the interest level high.