In 2006, the National Association of School Nurses (NASN) commissioned the largest and, to my knowledge, most recent national survey on the availability of nursing services in U.S. public schools. It was administered to a sample of over 1,000 schools in all 50 states and D.C.
The primary purpose was to gather basic information on the health staff in these schools, as well as a few core characteristics, such as school size and student demographics.
I must confess that I was a little surprised by the results. Here is the distribution of schools by nursing availability, summarized very briefly (these proportions vary by school size, type and other characteristics):