Humanism has been defined to be a religion by the United States Supreme court. With the help of this link and this link (Just search on "humanism and religion"), I was able to find the citation.

It is "Torcaso vs. Watkins 367 U.S. 488, 495 (1961)". This fellow didn't want to swear, "So help me God", because he didn't believe in God. The court decided in his favor because there were religions that didn't have a god. "Among religions in this country which do not teach what would generally be considered a belief in the existence of god are Buddhism, Taoism, Ethical Culture, Secular Humanism and others. See Washington Ethical Society v. District of Columbia, 101 U.S. App. D.C. 371, 249 F.2d 127; Fellowship of Humanity v. County of Alameda, 153 Cal. App. 2d 673, 315 P.2d 394; II Encyclopaedia of the Social Sciences 293; 4 Encyclopaedia Britannica (1957 ed.) 325-327; 21 id., at 797; Archer, Faiths Men Live By (2d ed. revised by Purinton), 120-138, 254-313; 1961 World Almanac 695, 712; Year Book of American Churches for 1961, at 29, 47."

This above was used to create the "conscientious objector" status used during the Viet Nam war -- on the basis of freedom of (Humanist) religion.

In 1987, the Christians tried to use the Humanist's own "separation of religion from state" against them by saying the account of creation in the Bible should have equal time to the religious teaching of evolution by the Humanists. Fair is fair.

That case was "Edwards v. Aguillard 482 U.S. 578 (1987)". The Humanists realized they were being hoist on their own petard and had to admit the Christians were right. "As the majority recognizes, ante, at 592, Senator Keith sincerely believed that "secular humanism is a bona fide religion," 1 App. E-36; see also id., at E-418; 2 id., at E-499, and that "evolution is the cornerstone of that religion," 1 id., at E-418; see also id., at E-282; id., at E-312 - E-313; id., at E-317; 2 id., at E-499. The Senator even told his colleagues that this Court had "held" that secular humanism was a religion. See 1 id., at E-36, id., at E-418; 2 id., at E-499. (In Torcaso v. Watkins, 367 U.S. 488, 495, n. 11 (1961), we did indeed refer to "Secular Humanism" as a "religio[n].") Senator Keith and his supporters raised the "religion" of secular humanism not, as the majority suggests, to explain the source of their "disdain for the theory of evolution," ante, at 592, but to convince the legislature that the State of Louisiana was violating the Establishment Clause because its teachers were misrepresenting evolution as fact and depriving students of the information necessary to question that theory. 1 App. E-2 - E-4 (Sen. Keith); id., at E-36 - E-37, E-39 (Sen. Keith); id., at E-154 - E-155 (Boudreaux paper); id., at E-281 - E-282 (Sen. Keith); id., at E-317 (Sen. Keith); 2 id., at E-499 - E-500 (Sen. Keith). The Senator repeatedly urged his colleagues to pass his bill to remedy this Establishment Clause violation by ensuring state neutrality in religious matters, see, e. g., 1 id., at E-36; id., at E-39; id., at E-313, surely a permissible purpose under Lemon. Senator Keith's argument may be questionable, but nothing in the statute or its legislative history gives us reason to doubt his sincerity or that of his supporters."

However, they couldn't decide against their own religion, so they decided against the Christians.
"Held:
1. The Act is facially invalid as violative of the Establishment Clause of the First Amendment, because it lacks a clear secular purpose. Pp. 585-594.
(a) The Act does not further its stated secular purpose of "protecting academic freedom." It does not enhance the freedom of teachers to teach what they choose and fails to further the goal of "teaching all of the evidence." Forbidding the teaching of evolution when creation science is not also taught undermines the provision of a comprehensive scientific education. Moreover, requiring the teaching of creation science with evolution does not give schoolteachers a flexibility that they did not already possess to supplant the present science curriculum with the presentation of theories, besides evolution, about the origin of life.
b) The Act impermissibly endorses religion by advancing the religious belief that a supernatural being created humankind.
2. The District Court did not err in granting summary judgment upon a finding that appellants had failed to raise a genuine issue of material fact. Appellants relied on the "uncontroverted" affidavits of scientists, theologians, and an education administrator defining creation science as "origin through abrupt appearance in complex form" and alleging that such a viewpoint constitutes a true scientific theory. "

In other words, they couldn't allow the Christian articles of faith to be promoted, even to an equal level in the schools. They stated (probably tongue-in-cheek) that creation can be freely taught in the schools without a law forcing it.
This law definitely lacked a secular [Humanist] purpose, as they said. It would have done major damage to their efforts of proselyting in the schools. But they did not deny that Humanism (which is taught in the schools) is a religion.

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What, pray tell, is "evolution"?
"Evolution" has many definitions, depending on the gullibility of the listeners. To separate out the homonyms, let us give each one a separate name.

"evolution(1)" is the basic idea that in the geological record, some life forms appeared and some have disappeared.

"evolution(2)" is the expansion that the life forms have mutated over time.

"evolution(3)" is the idea that the mutations occurred gradually over very long periods of time.

"evolution(4)" is the idea that life forms have gotten more complex over a long time solely due to competition for survival.

"evolution(5)" is the idea that life forms originated from non-living chemical and physical reactions by random chance.

"evolution(6)" is Carl Sagan's idea that the properties of chemistry and physics were randomly generated from the latest big bang, and the random consequences of that random occurrence over large amounts of time have ended up as life and us.

In the scientific community, evolution(3) is being quietly debated. On one side are geologists who declare that the whole archeological record has been pieced together. They have found no evidence of interspecies mutations between each of the catastrophes that mark the end of each era. New forms appear suddenly and fully formed, with few changes until the next catastrophe. On the other side are the evolution(4), (5) & (6) people whose faith depends on evolution(3) being true. They control the education establishment, so they keep teaching evolution(3) as fact, despite the facts. Galileo must be rolling over in his grave.

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Another law case:
Peloza vs. Capistrano Unified School District, 37 f.3d 517 (9th Cir. 1994)

Peloza held that he had been harassed and intimidated to force him to teach evolution, a religious tenet of Humanism, against his religious convictions. Unfortunately, Peloza had mentioned evolution(1) in his case, which was based on having to teach evolution(5). This hostile circuit court declared that there was no material damage, since he had merely been harassed and intimidated. They declared he couldn’t make up his mind as to what evolution was. On those two points, they threw the case out as frivolous and demanded he pay the school district’s legal costs. They also falsely declared, "We reject this claim because neither the Supreme Court, nor this circuit, has ever held that evolutionism or secular humanism are `religions' for Establishment Clause purposes."  On appeal, the appellate court stated his case had merit and threw out the requirement to pay the school district’s legal costs. However, they failed to decide in his favor....   The Supreme Court refused to review the case.

Peloza's biggest mistake was to decide to sue before getting good legal advice.  For good legal advice and support for American Christian teachers, contact:  American Center for Law and Justice.

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Attorneys for the Alliance Defense Fund filed suit Monday (November 22, 2004) against the Cupertino Union School District for prohibiting a teacher from providing supplemental handouts to students about American history because the historical documents contain some references to God and religion.

"Throwing aside all common sense, the district has chosen to censor men such as George Washington and documents like the Declaration of Independence," said ADF Senior Counsel Gary McCaleb. "The district's actions conflict with American beliefs and are completely unconstitutional."

Patricia Vidmar, principal of the Stevens Creek School, reportedly ordered the teacher, Stephen Williams, to submit his lesson plans and supplemental handouts to her for advance approval. Aside from Williams, a Christian, no other teachers were subject to the advance-screening requirement, says the ADF.

Just what documents did Williams submit that were deemed unfit for the school's students?

"Excerpts from the Declaration of Independence, the diaries of George Washington and John Adams, the writings of William Penn, and various state constitutions," said the public-interest law firm representing Williams.

"Less than 5 percent of all of Mr. Williams' supplemental handouts distributed throughout the school year contain references to God and Christianity," McCaleb said. "The district is simply attempting to cleanse all references to the Christian religion from our nation's history, and they are singling out Mr. Williams for discriminatory treatment. Their actions are unacceptable under both California and federal law."

California's Education Code does allow "references to religion or references to or the use of religious literature … when such references or uses do not constitute instruction in religious principles … and when such references or uses are incidental to or illustrative of matters properly included in the course of study."

The case, Stephen J. Williams v. Cupertino Union School District, et al., was filed in the U.S. District Court for the Northern District of California, Oakland Division.  All but the "equal protection" clause were thrown out April 28, 2005.  A new suit was quickly made up on only that clause.   On May 13, 2005, the court found in favor of Williams and passed injunctions against the Cupertino school district to not stifle Christians who admit to their faith.

see this link and this link for more information.

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On December 14, 2004, civil rights groups sued a Pennsylvania school district on Tuesday to block teaching of "intelligent design," an alternative to evolution that contends nature was created by an all-powerful being.  The case is called, "Kitzmiller v. Dover Area School District."   For the case, see this link.

The American Civil Liberties Union and Americans United for Separation of Church and State filed suit in federal court on behalf of parents of students in the Dover Area School District who object to the teaching of "intelligent design" alongside evolution in high school biology classes.

The suit claims the policy -- adopted by the board in October and to become part of the curriculum in January -- illegally promotes religious beliefs under the guise of science education.

The case was decided on December 20,2005 against the defendants.  Judge Jones found that intelligent design is a religious, non-scientific proposition, and that teaching intelligent design in public schools violates the Establishment Clause of the First Amendment.  He did not address whether the evolution being taught the children was not also religious and non-scientific.

As a devout Humanist, Judge John E. Jones wrote, “The proper application of both the endorsement and Lemon tests to the facts of this case makes it abundantly clear that the [School] Board’s ID [‘intelligent design’] Policy violates the Establishment Clause. In making this determination, we have addressed the seminal question of whether ID is science. We have concluded that it is not, and moreover that ID cannot uncouple itself from its creationist, and thus religious, antecedents….As stated, our conclusion today is that it is unconstitutional to teach ID as an alternative to evolution in a public school science classroom... . The breathtaking inanity of the Board’s decision [to adopt the ID Policy] is evident when considered against the factual backdrop which has now been fully revealed through this trial. The students, parents, and teachers of the Dover Area School District deserved better than to be dragged into this legal maelstrom, with its resulting utter waste of monetary and personal resources.” (pages 136–138)

For more information on this case (if you weren't inundated with the Humanist media's crowing about a victory), see this link.

See This Link for more information on secular Humanism..