I'm trying to write an expression that will calculate a childs current school year from their date of birth

I currently use
Code:
=DateDiff("yyyy",[Birthdate],Now())+Int(Format(Now(),"mmdd")<Format([Birthdate],"mmdd"))
to calculare their age which works fine.

I saw somthing here http://www.pcreview.co.uk/forums/thread-1171222.php but i couldnt get it to work. The principle seems to be to compare the date of birth to a base date that the school year is gudged from (i.e august first) then subtract 5 as school starts at age 5.

my birth date field is: Birthdate

basically i need somthing i can drop into a text box on a form that will give me the school year from date of birth

anyone with access brain got any ideas?