One of the things I have found very helpful as a parent and as a teacher, is a packet given to parents at the beginning of the school year to show what concepts will be learned and how the children learn those concepts. Since ways of teaching math have changed dramatically over the years, it is important for parents to be on the same page as the children. The way a parent may have learned to add multiple digit numbers may be greatly different from the way their child has learned to do the same task. Parents will need some background as to how the children are taught those concepts before even helping their children. Therefore, a packet outline all the concepts covered throughout the year may be helpful, as a starting point.
Sending home a second math book for parents to look at may also help. Seeing exactly how the children are learning the concepts is also important. If a second math book is not available, holding parent classes to teach the parents the concepts may also be a valuable ...
This posting covers different ways in which teachers(and parents) help children figure out and understand difficult math concepts.