Education
A 501(c)(3) organization may be organized and operated exclusively in furtherance of an educational purpose, but it is unclear to many startups what qualifies as educational. The first place to look is Treasury Regulation Section 1.501(c)(3)-1(d)(3), which provides that educational relates to:

(a) The instruction or training of the individual for the purpose of improving or developing his capabilities; or

(b) The instruction of the public on subjects useful to the individual and beneficial to the community.

An organization may be educational even though it advocates a particular position or viewpoint so long as it presents a sufficiently full and fair exposition of the pertinent facts as to permit an individual or the public to form an independent opinion or conclusion. On the other hand, an organization is not educational if its principal function is the mere presentation of unsupported opinion.

I recently had an IRS agent require that an applicant for 501(c)(3) status that plans to educate the public on global warming state that it will do so following the requirements described in the methodology test for determining if an organization's materials are educational rather than propaganda. Rev. Proc. 86-43. The test focuses on "the method used by the organization in advocating its position, rather than the position itself." IRS agents are instructed to conduct a review of the organization's materials for factors that show whether it fails to provide a:

A. Factual foundation for the viewpoint it advocates; or

B. Development from the relevant facts that would materially aid a listener or reader in a learning process.

Agents may also review the materials issued by the organization for the following factors, any of which may suggest that the organization may be engaged in propaganda rather than education:

A. The presentation of viewpoints unsupported by facts is a significant portion of the organization's communications;

B. The facts that purport to support the viewpoints are distorted;

C. The organization's presentations make substantial use of inflammatory and disparaging terms and express conclusions more on the basis of strong emotional feelings than of objective evaluations; and

D. The approach used in the organization's presentations is not aimed at developing an understanding on the part of the intended audience or readership because it does not consider their background or training on the subject matter.

See the Internal Revenue Manual, Exempt Organizations Examination Guidelines, Educational Organizations Other Than Schools.

UPDATE:  Congressional Research Service, 501(c)(3) Organizations: What Qualifies as 'Educational'? (August 21, 2012)