Using data from this U.S. 2006 Department of Education report, the graph above (click to enlarge) shows average tuition at private schools (elementary and secondary) vs. average per pupil spending for public schools (elementary and secondary) for the 2003-2004 school year.
Average private school tuition ($6,600) was about 1/3 less than the spending per pupil in public schools ($9,620) in 2003-2004 (the most recent year available), and average Catholic school tuition ($4,254) was less than half of public school spending per student.
Not only was the average private school tuition between 1/3 and 1/2 less than the cost per public school student, the private schools had on average 18% more teachers per 1000 students (72.25 in private schools vs. 61 in public schools) in 2003-2004.
Bottom Line: Private schools can educate students at a lower cost, with more teachers per 1000 students, than the public schools. Reason: Private schools must have significantly fewer non-instructional administrative employees, and therefore significantly lower administrative expenses than their public counterparts.