" I have current Texas Math (K-8) and Chinese (K-12) certificates. I am good at mental math and critical thinking. In Math, students need to speed up for tests and make sure they do right. I have been a math teacher at a local school and a math mentor at a middle school, Austin ISD. American schools focus on the use of manipulatives and calculators and computers. This is right. But when too much attention is given at the sacrifice of independent brain activity (mental math), the students cannot d"