Sanderson was born and brought up outside the British public-school system that he was to affect so profoundly. His early education was obtained in a parish school. His father was employed in the estate office of Lord Boyne at Brancepeth in Durham. There were several brothers but they all died before manhood, and the scanty indications one can glean of those early years suggest a slender, studious, and probably rather delicate youngster. He was never very proficient in any out-of-door games. In the early days at Oundle he careered about on a bicycle; in later years he played tennis; his vacation exercise was rock-scrambling. He became a 'student-teacher,' so the official Life phrases it, at a school at Tudhoe, but whether there was any difference between being a student-teacher at a school at Tudhoe and being an ordinary pupil-teacher in an ordinary elementary school under the English Education Department I have been unable to ascertain. He was already notable in his village world as exceptionally intelligent, industrious, and ambitious, and with a little encouragement from the local vicar and one or two friends he effected an escape from the strangling limitations of elementary teaching. He may have aimed at the church at that time. At any rate he gained a scholarship and entered Durham University as a theological student. He did well in Durham University both in theology and mathematics; he was made a Fellow and he was able to go on as a scholar from Durham to the wider and more strenuous academic life of Cambridge. At Cambridge theology drops out of the foreground of the picture. He took a fairly good degree in mathematics, and he worked for the Natural Science Tripos. He did not fight his way up into that select class which secures Cambridge fellowships, but he had made a reputation as an able, hard, and honest worker; he was much sought after as a coach, and he was given a lectureship in the woman's college of Girton. From this he went as senior physics master to the big school for boys at Dulwich. A photograph of him in the early Dulwich period shows him slender and keen-looking, already bespectacled and with a thick moustache; except for the glasses not unlike another ruddy north-countryman I once knew, the novelist George Gissing. Both were what one might call Scandinavian in type. But Gissing was as despondent as Sanderson was buoyant. In those days, an old Dulwich associate tells me, Sanderson was in a state of great mental fermentation. He loved long walks in his spare time, and along the pebbly paths and roads and up and down the little hills of that corner of Kent, the two of them talked out a hundred aspects and issues of the perplexing changing world in which they found themselves.