My D15 has always had this issue with math facts tests. She also had CTY level scores in math (along with very high verbal scores). She was ultimately diagnosed with a non-verbal learning disability, and the two biggest "symptoms" we see in every day life are slower processing speed on math facts and problems with executive functioning. Honestly, once they get to middle school, this issue fades somewhat. We have asked for extra time on math tests for her with her school, and because of the diagnosed learning disability they have readily given her that when needed. She also has been granted extra time on College Board tests (SAT, SAT Subject, and AP).