Before they were abolished in 1904, to be replaced by the London County Council as the authority in charge of London schools, the School Board for London produced a large printed report that includes a history of the development of its school buildings over the years since 1870. (Their achievement was impressive. There were no publicly provided schools when they started; over their 34 years they built 469.) One of the schools mentioned as significant was Mina Road (1882), and they print its plan, evidently of the first floor, where the Boys’ department was housed:
(Final report of the School Board for London 1870-1904, 1904, p.63.)
From other things I've read it seems the basic class size was 60, though it could be subdivided into 2 x 30 as we see in two of the classrooms, or doubled up for teaching by the head teacher, with one or more pupil-teachers, in the hall -- which had desks for that number. The broken line represents the ‘rolling shutters’ that were later removed. The principle was that the head teacher should be able both to teach one or two classes in the hall and keep an eye on the assistant teachers and pupil-teachers in the classrooms.
The total accommodation for that floor, going by the numbers on that plan, was 420 pupils (boys, not infants, aged 7-12) in 7 classes of 60 - and that fits with the actual pupil numbers I've found recorded in documents at the National Archives in Kew.
Mina Road was not judged a success. The Board’s account is as follows:
ln order to combine teaching with the occasional use of a large room for collective purposes, two types were now tried; one the Mansford-street (Hackney S) and Mina-road (East Lambeth K) type, of which four schools were built. Here there were large halls available for infants and for boys, but each of them were occupied permanently by two classes and the corresponding rooms for the girls were supplied on a separate floor over the hall. This type, though providing two handsome rooms, was not serviceable for teaching or for assembling the children. These schools are being improved by the halls being freed from the classes and used for their special purpose. (Final Report p.37)
That improvement was made possible by the removal of the oldest classes (Standards 5 and 6, what would later be called 1st and 2nd year secondary and now Year 7 and 8) to the new building, that still stands. Quite what was meant by that account of the girls’ provision on the second floor isn’t clear to me.
I hope the original plans survive in the archives. Patrick Kingwell and I will be looking in the London Metropolitan Archives -- we’ll report if we find them.