Determine at the beginning of the school year that you or your child will keep up to speed and more and not lag behind in math in any way. Work with the teacher and talk about your child. Ask for a diagnostic test.
Take a look at your child's math textbook. There will be a lot of topics in there that the child will be expected to have some level of understanding about by the end of the year. Review the book for yourself and your child.
Ask a friend who is good in math, if you aren't yourself, or a math tutor to find your weak areas, if there are any.
Set up a study time for a half an hour or an hour a few days a week. During this time have your child work on her weak areas. It may be in geometry, graphs, fractions, subtraction with borrowing, conversions or money. Give your child the opportunity to master the math areas she is expected to know at this grade level. And when the time of the time of the real test comes, your child will pass the TAKS test.