Besides fossils, he collected not only butterflies, as do most boys at some time or other, but also birds; and he with his sister Alice, being instructed in the art of preparing and preserving skins, succeeded in making a very considerable collection. He thus acquired before long not only a very large but a very exact knowledge of British birds.
In the more ordinary work of the school-room he was somewhat backward. This may have been partly due to the great difficulty he had in learning to write, for he was not only left-handed but, in his early years, singularly inapt in acquiring particular muscular movements, learning to dance being a great trouble to him. Probably however the chief reason was that he failed to find any interest in the ordinary school studies. He fancied that the family thought him stupid, but this does not appear to have been the case.
In character he was at this time quick tempered, sometimes even violent, and the energy which he shewed in after life even thus early manifested itself as perseverance, which, when he was crossed, often took on the form of obstinacy, causing at times no little trouble to his nurses and tutors. But he was at the same time warm-hearted and affectionate; full of strong impulses, he disliked heartily and loved much, and in his affections was wonderfully unselfish, wholly forgetting himself in his thought for others, and ready to do things which he disliked to please those whom he loved. Though, as we have said, somewhat clumsy, he was nevertheless active and courageous; in learning to ride he shewed no signs of fear, and boldly put his pony to every jump which was practicable.
In 1861 he was sent to the Rev. C. G. Chittenden's preparatory school at Hoddesden in Hertfordshire, and here the qualities which had been already visible at home became still more obvious. He found difficulty not only in writing but also in spelling, and in the ordinary school-work he took but little interest and made but little progress.
In 1865 he was moved to Harrow and placed in the house of the Rev. F. Rendall. Here, as at Hoddesden, he did not show any great ability in the ordinary school studies, though as he grew older his progress became more marked. But happily he found at Harrow an opportunity for cultivating that love of scientific studies which was yearly growing stronger in him. Under the care of one of the Masters, Mr G. Griffith, the boys at Harrow were even then taught the elements of natural science. The lessons were at that time, so to speak, extra-academical, carried on out of school hours; nevertheless, many of the boys worked at them with diligence and even enthusiasm, and among these Balfour became conspicuous, not only by his zeal but by his ability. Griffith was soon able to recognize the power of his new pupil, and thus early began to see that the pale, earnest, somewhat clumsy-handed lad, though he gave no promise of being a scholar in the narrower sense of the word, had in him the makings of a man of science. Griffith chiefly confined his teaching to elementary physics and chemistry with some little geology, but he also encouraged natural history studies and began the formation of a museum of comparative anatomy. Balfour soon began to be very zealous in dissecting animals, and was especially delighted when the Rev. A. C. Eaton, the well-known entomologist, on a visit to Harrow, initiated Griffith's pupils in the art of dissecting under water. The dissection of a caterpillar in this way was probably an epoch in Balfour's life. Up to that time his rough examination of such bodies had revealed to him nothing more than what in school-boy language he spoke of as "squash;" but when under Eaton's deft hands the intricate organs of the larval Arthropod floated out under water and displayed themselves as a labyrinth of threads and sheets of silvery whiteness a new world of observation opened itself up to Balfour, and we may probably date from this the beginning of his exact morphological knowledge.