C2 grade sounds like the kind of grade issued in the Ireland 11+ exams. It essentially means that your child is in the top 45% percentile of everyone who took the examination.
In Ireland you are issued a grade as follows:
Grade A to 25% of all pupils in that year group who get the highest marks
Grade B1 to the next 5% of pupils
Grade B2 to the next 5% of pupils
Grade C1 to the next 5% of pupils
Grade C2 to the next 5% of pupils
Grade D to the remainder of pupils who sat the examination
You can get a fuller explanation of the Northern Ireland eleven plus exam system (due to be scrapped in 2008) on the following link:
http://www.elevenplusexams.co.uk/11-plu ... reland.php
Hope this helps.