In the fall of 2007, about 73.7 million people were enrolled in American schools and colleges (table 1). About 4.6 million people were employed as elementary and secondary school teachers and as college faculty, in full-time equivalents (FTE). Other professional, administrative, and support staff at educational institutions totaled 5.2 million. All data for 2007 in this Introduction are projected. Some data for other years are projected or estimated as noted. In discussions of historical trends, different time periods and specific years are cited, depending on the timing of important changes as well as the availability of relevant data.
link to more info: http://nces.ed.gov/programs/digest/d07/