Parents no matter how good they are do not have enough knowledge to combat difficult questions simply because they themselves havnt mastered the techniques
But parents can master the techniques - the IPS booklet on how to teach the various types of VR for example is fantastic and certainly taught me as did lots of very helpful posts on here. My mother, who helped tutor DD on days she picked her up from school, even went to the extent of doing the papers before DD to make sure she knew how to answer each question!
Having used a tutor who turned out to be not very good you need to be very sure about a tutor you use or DIY when as others have said you can quickly and easily work on weaknesses. I am DIY ing with DS as he needs lots of small chunks rather than a full hour. Spent last weekend surrounded by Patricia's 'compound word cards' trying to work them all out - DS loved it altho I'm not sure that making up phrases such as 'get a life' are quite the idea