I really enjoyed reading this article: http://www.usnews.com/education/blogs/high-school-notes/2016/04/11/dos-donts-for-parents-to-help-teens-build-math-interest-and-success
A summary:
- Don’t project negative feeling toward math onto teens
- Do talk to teens and teachers about what’s being taught in math class
- Don’t be too quick to hire a tutor for struggling students
- Do support students with the right tools
I recommend the whole article and the references therein.