There is one at Tiong Bahru Community Centre called Nanyang Educational Consultancy. My boy normally averages around B grade for Maths(early P5) and Problem Sums was robbing him of alot of marks. Then we tried a couple of tuition centres but it did not work out until my friend recommend me to try Nanyang. My boy learned some techniques here (for eg he would show me how guess n check could be done better than school method) Eventually by P6 SA1, my boy got an A. And for PSLE, he got an A* for Maths. He got into NUS High School of Maths and Science. You might want to try. This centre is already very popular for their Maths and Science classes. One thing I like about them is no matter how popular their class is, they kept to a maximum of six students. The rate is slightly more expensive but I think it is worth it.