AK Whitney, is a freelance journalist and former math hater in Southern California
The biggest favor anyone can do a kid struggling with math is to throw out any notions that it's intuitive, or that you have to have a gift for it to do well, as in, "oh, he or she is a math genius!" Would you ever say that to someone about reading? Math is NOT just for geniuses, and most of us use it every day, even if it's just counting your change at the market.
Unless your child is struggling with a math disability such as dyscalculia (and that's hard enough to diagnose, but a big indicator is if the child has trouble telling that 8 is a bigger quantity than 3), he or she should be able to learn math. Remember, even the most impressive mathematicians have struggled in school at times.
It's perfectly fine to acknowledge that yes, this is going to take some work, but there's no reason they can't learn it. This is particularly important for girls, who all too often get the message that their gender means they can't do math. On a more practical level, a lot of the time kids struggle with a new concept because their foundational skills are cracked. For example, fractions mess up a lot of people because they need a strong sense of quantity and place value, and involve addition, subtraction, multiplication and division. Going back and reviewing those skills can help, as well as helping relate them to this new way of thinking, will help. For more information, I would suggest you check out Stanford psychologist Carol Dweck's book, "Mindset." Dweck worked with middle schoolers in the '80s and showed that their math scores tended to improve when they were told math ability was not set in stone. Also, check out my primer on dyscalculia for Mental Floss. And finally, please read this profile on the first woman to win the prestigious Fields Medal, Maryam Mirzakhani. Best of luck!