This article is from the Aviation FAQ, by Geoffrey G. Peck email@example.com with numerous contributions by others.
Multiple commercial vendors offer computerized testing with results
available immediately after you finish the test. Costs range from $40
to $85 for a test. To find out where your nearest testing center is
and to schedule a test, contact one of
Lasergrade Computer Testing <http://www.lasergrade.com>
1-800-211-2754 or 1-360-896-9111,
Aviation Business Services (Computerized Aviation Testing Service)
1-800-947-4228 or 1-415-259-8550, or
Sylvan/Prometric 1-800-359-3278, 1-800-967-1100, 1-612-896-7702 or
You will need a written authorization before you can take most FAA
tests. This may be obtained from an appropriately rated and
FAA-Certificated Flight Instructor or Ground Instructor, or, if you
completed a home-study course, with some difficulty you can get your
local FSDO to sign you off.