According to this article the oldest child has the higher IQ and and the youngest child in the family the lowest.
www.timesonline.co.uk/tol/life_and_style/health/article3729274.ece
Obviously I used agree being the elder child.
However, with my own children not so sure. DS1 seems more 'academic' (lol at 4 yrs) whilst DD aged 2 exhibits a scary criminal intelligence that's more calculated than anything ds can do.
..or is this just pseudo science?