Season of Birth as an Instrument

The use of season of birth as an instrument for education is something that has been debated in Economics for the last 20 years or so, with the basic idea being that season of birth is randomly distributed but can effect school attainment through timing of compulsory school and so on (see the original Angrist and Krueger paper and recent work referenced in the paper below for a much more eloquent summary). A number of papers, particularly Bound and Jaeger (1995) argue the relationship between season of birth and schooling is too weak for it to be used as an instrument. A recent NBER paper by Buckles and Hungerman provides a new argument as to why this instrumentation strategy may not be valid, namely that people with different socioeconomic characteristics time their conceptions differently.