The biggest blunder most of them as parents make while teaching is using their time tested methods or their vision about a subject or topic and forcing the child to follow same. If the child fails to response or is looking for another way to get to the same topic the parent is irritated of not being able to get across the topic in the way decided.
Many topics in Maths or English grammar which are logical can be broken down into many different methods. But parents have learned through a method during their times and have their concept or views and want the child to see through the same . The logic and IQ with which you learnt need not be same for the child . Hence its very important to recheck on your methods if the child isn’t getting even after repeated explainations.
Leave the topic for the day or few hours and return back fresh with a new path and attitude and see the child actually understand. Its understandable everyone doesn’t have much time , but one can always find time to slip in loads of content on every topic available on net based on depth and age .Then decide on the right way to get the childs study done.