Where can I find a list of all high schools, public and private, in
the US (in a properly formatted file -- a table, or excel
spreadsheet).

Hi ajnet,

The most comprehensive database for high schools in the US can be
located at the National Center for Education Statistics website:
http://nces.ed.gov/


Public Schools: 
http://nces.ed.gov/ccd/schoolsearch/

Enter the criteria you specify and click search. For example, I
selected Louisiana in the 'State' category, and left all the other
information blank in "School Information".

Under "Additional Characteristics" I selected:
School Description - Regular
Specific School Type - All
Grade-Span - Includes Grades: All, Low Grade: 7, High Grade: 12 

The result is a list of 283 Public Schools that can be downloaded into
an Excel File. At the bottom of the page, you will see this option.
Just click on Download Excel File and save it.


Private Schools:
http://nces.ed.gov/surveys/pss/privateschoolsearch/

As above, enter the specific criteria you wish. The data can also be
downloaded into an Excel File as mentioned above.


Search strategy:
personal bookmark

I hope this is is helpful. If you have any questions regarding my
answer please don?t hesitate to ask before rating it.

Best regards,
Rainbow

thanks!