Accounts of Sanderson's work in Dulwich school differ very widely. At one time it would seem that he had troubles about discipline, and it is quite conceivable that his methods there were experimental and fluctuating. No doubt he was trying over at Dulwich many of the things that were to establish his success at Oundle. On the whole the Dulwich work was good work, and it gave him sufficient reputation to secure the headmastership of Oundle School when presently the governing body of that school sought a man of energy and character to modernise¹ it.  
The most valuable result of his Dulwich period was the demonstration² of the interestingness of practical work in physical science for boys who[Pg 22] remained apathetic³ under the infliction⁴ of the stereotyped⁵ classical curriculum. He was not getting the pick of the boys there but the residue⁶, but he was getting an alertness and interest out of this second-grade material that surprised even himself. The interest of the classical teaching was largely the interest of a spirited competition which demanded not only a special sort of literary ability but a special sort of competitive disposition⁷. But there are quite clever boys of an amiable⁸ type to whom competition does not appeal, and some of these were among the most interesting of the youngsters who were awakened⁹ to industrious¹⁰ work by his laboratory instruction.
 
It is clear that before Sanderson went to Oundle he had already developed a firm faith in the possibility of a school with a new and more varied¹¹ curriculum, in which a far greater proportion of the boys could be interested in their work than was the case in the contemporary classical and (formal) mathematical school, and also that he had conceived the idea of replacing the competitive motive¹², which had ruled the schools of Europe since the establishment of the great Jesuit schools three hundred years before, by the more[Pg 23] vital stimulus¹³ of interest in the work itself. He also took to Oundle a proved and tested conception of the need for the utmost possible personal participation¹⁴ by every boy in every collective function of the school. Quite early in his Oundle career he came into conflict with his boys and carried his point upon the issue whether every boy was to sing in the school singing or whether that was to be left to the specialised choir¹⁵ of boys who had voices and a taste for that sort of thing. That was an essential issue for him. From the very first he was working for the rank and file and against the star system of school work by which a few boys sing or work or play with distinction and encouragement, against a background of neglected shirkers and defeated and discouraged competitors.
 
Sanderson married soon after he went to Dulwich. His wife came from Cumberland and she excelled in all those domestic matters that made a successful headmaster's wife. Throughout all the rest of his life she was his loyal and passionate¹⁶ partisan¹⁷. His friends were her friends, and his critics and opponents were her enemies, and if she had a fault it was that she found it difficult[Pg 24] to forgive any one who had seemed ever to differ from him. Two sons were born during the seven years that passed in the little home in Dulwich. It must have been a very brisk and happy little home. One can imagine the tall young man with his gown a little powdered with blackboard chalk, flying out behind him, striding along the school corridors to some fresh and successful experiment in laboratory work, or in homely¹⁸ tweeds walking along the Kentish lanes with his friend, or snatching a delightful¹⁹ half-hour in the nursery to see Master Roy's first attempts to walk, or reading some new and stirring book with the lamp of those days before electric lighting²⁰ at his elbow. He was thirty-five when he achieved his last step in the upward career of a secondary schoolmaster and was appointed headmaster of Oundle. That success probably came as a surprise, for Sanderson's modest origins and the fact that he was not in holy orders must have been a serious handicap upon his application. It must have been a very elated young couple who packed their household belongings²¹ for the unknown town of Oundle.