I have a non-profit and website that helps school teachers find sorely
needed school supplies for the classroom. One of the things I want to
show donors is the percent of the school-teacher's school population that
is on the free lunch program. For instance, I want to show on the
school home page or the teacher's home page that (for instance) 28% of
the students at the school qualify for the free lunch program.

I can already find out if *some* or *all* of the school students
qualify for the free lunch program. I can get this info from
nces.ed.gov, which seems to be the best source. However this number is
not helpful. I want to be able to give donors the ability to see the
actual percentage of students that are poor. When giving a piano I
want the donor to see that 85% of a school is on the free lunch
program vs. another school of 22%. The donor can then decide which
school is better suited for their donation.

Another site similar to mine shows the percentage of low income
residents at the school. They have a pop-up that says:

["low income" refers to the percentage of students at a given school
who qualify for free lunch, which is considered a measure of economic
need. To be deemed eligible for free lunch, a student must submit a
form showing family income at or below 130% of the poverty line. In
2001, a student in a family of 4 received free lunch if the family
income was $23,530 or less.] (this actual poverty level is higher now)

I do not want to use census numbers to calculate the school's zip code
and poverty levels. This doesn't work because many of America's
students are bussed into schools. I currently show the "Average
Household Income" for the school. Many teachers don't like this number
because it reflects the school's zip code demographics and not the
actual student population's demographics.

So, my question is "What is the source for an actual database for all of
America's public schools that contains at a minimum the (National
Center for Education Statistics) NCES-ID# and the percentage of
students at that particular school that are qualified for the free
lunch program.

The free lunch program is part of (what's commonly referred to as)
'Title 1' of the No Child Left Behind Act.

If you have questions before submitting an answer please fire away. Thanks much!

I would set up a website for schools to register for donations. the
school would be ask a series of questions which includes percent of
student receiving free lunch. Target specific regions and send them
literature on you program i'm sure they will fill in the information
for you. On a side note the most needy schools in America are in new
orleans. before Katrina there were about 120 public schools, starting
this fall they will open 25 school mostly charter school. Most school
in new orleans are old 1 story building and were flooding destroying
all books, desks, and every other thing schools use. you name it they
lost it.

The raw Common Core Data (CCD) is available for download at 
http://nces.ed.gov/ccd/pubschuniv.asp

The data is contained within fixed-width flat files and the column
information is contained in the "Record Layout" file.  The data can be
imported into a database and made accessible to your website (note -
the files don't contain a data element for "percentage of students
that are religible for free/reduced lunch", but that metric can be
derived from the available data).

Hope this helps.