There has been considerable discussion on this in the past on Lactnet with
some great references. Have a look in the archives.  I refer you to Brian
Palmer's letter of April 17/96 for example.

Below are the references on Kathy Dettwyler's home page. Kathy please send
me a note and slap my fingers if you mind me pulling them off and posting it
here. It was faster than pulling them out of my references in the word
processer as I don't keep them by topic. >


>On IQ (and the lead analogy is based on "average IQ deficits" in children
exposed to lead in
>situations like old apartment buildings where the paint had lead in it. I
agree that IQ tests are suspect
>in general, but all of these studies have found small but significant
benefits to the breastfed children.
>Whatever talent it is that IQ tests measure, breastfed babies are much
better at it).
>
>Bauer, G. et al. 1991 Breastfeeding and cognitive development of
three-year-old children.
>Phychological Reports, 68:1218.
>
>Lucas, A., et al. 1992 Breast milk and subsequent intelligence quotient in
children born preterm.
>Lancet 339:261-264.
>
>Morley, R. et al. 1988 Mother's choice to provide breast milk and
developmental outcome.
>Archives of Disease in Childhood 63:1382-1385.
>
>Morrow-Tlucak, M. et al. 1988 Breastfeeding and cognitive development in
the first two years of
>life. Social Science and Medicine 26:635-639.
>
>Rodgers, B. 1978 Feeding in infancy and later ability and attainments: A
longitudinal study.
>Developmental Medicine and Child Neurology 20:421-426.
>
>Rogan, W.J., and B.C. Gladen 1993 Breastfeeding and cognitive development.
Early Human
>Development 31:181-193.
>
>Taylor, B., and J. Wadsworth 1984 Breastfeeding and child development at
five years of age.
>Developmental Medicine and Child Neurology 26:73-80.
>
>Temboury, M.C. et al. 1994 Influence of breastfeeding on the infant's
intellectual development.
>Journal of Pediatric Gastroenterology and Nutrition 18:32-36.
>
>