This website is devoted to research based practices to boost mathematics development in students. I highly recommend this as a place to start learning about ways to support your child, whether they love or hate math. 

This article documents several child psychology expiraments, showing how saying "You're really smart" has a different (and often negative) effect, as opposed to saying "You work really hard, huh?" 

This article outlines the research of Carol Dweck, who explains the benefits of having a "growth mindset." Basically, if students think that their brain is like a muscle, and that it can get stronger with more practice, they are more likely to succeed in math class. This is in contrast to the common belief that some people are just "math people," and other people are just born not strong in math.

This list provides a number of ways to talk to children about their hard work leading to success.