As an answer to question “Seminal papers that later were proven to contain errors”, @snoram mentioned Angrist and Krueger (1991), and there use of quarter of birth as an (exogenous) instrument for education.
@snoram illustrates using (Buckles and Hungerman, 2013) how quarter of birth is in fact correlated with important characteristics of the mother.
In a comment, @snoram write:
“For the record I think Angrist and Krueger's work is amazing, but today we know better than to use quarter of birth (in the us at least and for this purpose) as an instrument. Science advances.”
My question : which variables are know to be better than quarter of birth as instruments for, say, “years of schooling” (or more generally “education”)?