I was not sure as to the answer Lola. Research Ilooked at suggested anywhere between 3rd and 6th. It has changed over time. I am including two interesting article links, the first about target audiences iwth periodicals, and the second which should completely undercut what Rhonda was saying (I assume).
1. Article on periodicals and papers and target audiences published by Impact Information
Plain-Language Services http://www.impact-information.com:
http://www.impact-information.com/impactinfo/newsletter/plwork15.htm
2. Article on Palin's speaking vs. Biden's speaking:
http://features.csmonitor.com/politics/2008/10/04/palin-speaks-at-higher-grade-level-than-biden/