QUOTE(unmusicalmum @ Jan 23 2006, 07:53 PM)

For a given grade, is there an easy rule of thumb as to how difficult the sight reading is for it? I seem to remember being told you should be able to sight read pieces from 2 grades below where you are, but is that the level that is actually in the grade exam? My son has just skipped a piano grade and I'm wondering if his sight reading is going to be up to it.
It would be a good idea for your son to work through a sight-reading book for the grade he is skipping. As well as the ABRSM book mentioned above - there are several books available - Improve your Sight-reading, Perfect your sight-reading, Sight-reading for fun - one book per grade. It is better to improve sight-reading by starting with exercises that are easy and gradually increase in difficulty than start with a higher grade and struggle a bit. Perhaps you could ask his new teacher are there any books s/he would recommend for sight-reading practice.
I think grade 5 sight-reading is a bit more difficult than grade 2.