At school, his companions respected him heartily, and loved him for his unselfish kindness and sweetness, while a few of the more graceless were inclined to brand him as soft or slow, because he never consented to join in anything blameable, and was not devoted to boyish sports, though at times he would join in them with great vigour, and was always perfectly fearless.
From the Grange he passed to Cambridge, and was entered at St.John's, but finding that his Scottish birth was a disadvantage according to restrictions now removed, he transferred himself to Caius College.

He kept up a constant correspondence with his eldest sister, Mrs.Dundas, and from it may be gathered much of his inner life, while outwardly he was working steadily on, as a very able and studious undergraduate.

With hopes of the ministry before his eyes, he begged one of the parochial clergy to give him work that would serve as training, and accordingly he was requested to read and pray with a set of old people living in an asylum.

The effort cost his bashfulness much, but he persevered, with the sense that if he did not go "no one else would," and that his attempts were "better than nothing." This was the key to all his life.
At the same time he felt, what biography shows many another to have done, the influence of the more constant and complete worship then enjoined by college rules.

Daily service was new to him, and was accepted of course as college discipline, but after a time it gathered force and power over his mind, and as the _Magnificat_ had been a revelation to Henry Martyn, so Charles Mackenzie's affection first fixed upon the General Thanksgiving, and on the commemoration of the departed in the prayer for the Church Militant.
His fellow-collegians thought of him as a steady, religious-minded man, but not peculiarly devout, and indeed the just balance of his mind made him perceive that the prime duty of an undergraduate was industry rather than attempts to exercise his yet unformed and uncultivated powers.