Harvard (1833–1837; 16–20 y/o)

Harvard “nearly ruined him as a writer.”

Every term for three long years, Edward Tyrrel Channing, the Boylston Professor of Rhetoric and Oratory, issued Thoreau a long series of assignments, every one of which he collected, corrected, and returned, scored on Quincy’s merciless eight-point scale. If Thoreau kept a journal through these years, it is lost; if he wrote letters home, they are gone; when he ventured into poetry, his verses mostly vanished. What survives are his essays for Channing. They disappoint.
The young and earnest Henry Thoreau learned so well how to write for his teacher that it took ten years and a move to Walden Pond to shake himself free.

Orestes Brownson (1836; 19 y/o)

Thoreau’s association with Brownson broke the spell of Harvard.

This was Thoreau’s first encounter with a free-range intellectual for whom ideas snapped and crackled, who moved easily in the circles of the great and the near great. His term with Brownson broke the spell of Harvard.
To Thoreau, the scholarship boy struggling to pay his tuition bills, Brownson’s words hit home. To Brownson, education was the key to creating true equality, which meant the key to remedying all the evils of society. He didn’t mean reading, writing, and ciphering; he meant real education, “the formation of character, the moral, religious, intellectual, and physical training, disciplining, of our whole community.”
Thoreau was living with Brownson at the very moment he was writing his breakthrough book, New Views of Society, Christianity, and the Church, which soon joined Emerson’s Nature as a founding text of Transcendentalism.
Thoreau was testing out Transcendentalism on his own well before it existed as a movement.

Walls, Laura Dassow. Henry David Thoreau: A Life. First edition, University of Chicago Press, 2017.