Students are permitted and encouraged to use a calculator to review their work. According to the National Council of Teachers of Math (NCTM), "Appropriate instruction that includes calculators can extend students' understanding of mathematics and will allow all students access to rich problem-solving experiences." Calculators can support teachable moments. Once students notice a problem is incorrect after checking the answer with a calculator, they can review and fix the problem. This will practice their reflective and problem skills. Research evaluating 79 studies on the effectiveness of calculators confirms this position.