Most U.S. states adopted a version of the system Mann established in Massachusetts, especially the program for normal schools to train professional teachers.

[2] Educational historians credit Horace Mann, along with Henry Barnard and Catharine Beecher, as one of the major advocates of the Common School Movement.

[10][11] Mann defended James Allen in a robbery trial by placing a reasonable doubt in the minds of the jury by pointing out that the victim had previously identified someone else as the man who robbed him.

[12] Mann was elected to the Massachusetts legislature in 1827, and in that role was active in the interests of education, public charities, and laws for the suppression of alcoholic drinks and lotteries.

While in the legislature, he was a member and part of the time chairman of the committee for the revision of the state statutes, and a large number of salutary provisions were incorporated into the code at his suggestion.

As a member of the Senate, he spent time as the majority leader, and aimed his focus at infrastructure, funding the construction of railroads and canals.

Mann persuaded his fellow modernizers, especially those in the Whig Party, to legislate tax-supported elementary public education in their states and to feminize the teaching force.

[citation needed] He planned and inaugurated the Massachusetts normal school system in Lexington (which shortly thereafter moved to Framingham), Barre (which shortly thereafter moved to Westfield) and Bridgewater, and began preparing a series of annual reports, which had a wide circulation and were considered as being "among the best expositions, if, indeed, they are not the very best ones, of the practical benefits of a common school education both to the individual and to the state".

[19] By his advocacy of the disuse of corporal punishment in school discipline, he was involved in a controversy with some of the Boston teachers that resulted in the adoption of his views.

His six main principles were: Under the auspices of the board, but at his own expense, he went to Europe in 1843 to visit schools, especially in Prussia, and his seventh annual report, published after his return, embodied the results of his tour.

Instilling values such as obedience to authority, promptness in attendance, and organizing the time according to bell ringing helped students prepare for future employment.

[22] The practical result of Mann's work was a revolution in the approach used in the common school system of Massachusetts, which in turn influenced the direction of other states.

[25] A devotee of the pseudoscience of phrenology, Mann believed education could eliminate or reduce human failings and compensate for any biological flaws.

"[27] Like many nineteenth century reformers, Horace Mann believed that "children would find it far more interesting and pleasurable to memorize words and read short sentences and stories without having to bother to learn the names of the letters".

In 1940, one-third of high school students were incapable of mastering reading and writing well enough to profit from textbook instruction, and one half of the adult population in the United States was functionally illiterate".

[31] Upon becoming the secretary of education of Massachusetts in 1837, Mann worked to create a statewide system of professional teachers, based on the Prussian model of "common schools."

Historian Ellwood P. Cubberley asserts: No one did more than he to establish in the minds of the American people the conception that education should be universal, non-sectarian, free, and that its aims should be social efficiency, civic virtue, and character, rather than mere learning or the advancement of sectarian ends.

In the spring of 1848 he was elected to the United States Congress as a Whig to fill the vacancy caused by the death of John Quincy Adams.

His first speech in that role was in advocacy of its right and duty to exclude slavery from the territories, and in a letter, in December of that year, he said: "I think the country is to experience serious times.

"[38] During the first session, he volunteered as counsel for Drayton and Sayres, who were indicted for stealing 76 slaves in the District of Columbia, and at the trial was engaged for 21 successive days in their defense.

[39][40] Mann was defeated by a single vote at the ensuing nominating convention by Webster's supporters; but, on appealing to the people as an independent anti-slavery candidate, he was re-elected, serving from April 1848 until March 1853.

Mann considered there to be three legitimate methods by which the Africans in captivity in the US could emancipate themselves, including, as a last resort, that "such as our revolutionary fathers adopted against Great Britain [...] not only with the justification but with the approval of the civilized world.

The second condition will be fulfilled, either when the slaves believe they can obtain their freedom by force, or when they are so elevated and enlarged in their moral conceptions as to appreciate that glorious supplication of Patrick Henry, 'Give me liberty or give me death!'"

[41] In September 1852, he was nominated for governor of Massachusetts by the Free Soil Party, and the same day was chosen president of the newly established Antioch College at Yellow Springs, Ohio.

There he taught economics, philosophy, and theology; he was popular with students and with lay audiences across the Midwest who attended his lectures promoting public schools.

Mann also employed the first female faculty member to be paid on an equal basis with her male colleagues, Rebecca Pennell, his niece.

The young women chafed at restrictions on their behavior, and wanted to meet with men in literary societies, which Mann and his wife opposed.