This section is from the book "Modern Buildings, Their Planning, Construction And Equipment Vol3", by G. A. T. Middleton. Also available from Amazon: Modern Buildings.
The number of Classrooms should be sufficient for the requirements of the school. Classrooms should not be passage rooms from one part of building to another, or from schoolrooms to playgrounds or yard. Schoolrooms and classrooms must have independent entrances, and rooms should be so arranged that each can be easily cleared without disturbing work in another.
A classroom should not be planned for more than 50 or 60 children (in special cases larger rooms may be approved), and not less than 24 scholars. In absence of supplementary light, measurement from window wall in a room 14 feet high should not exceed 24 feet 8 inches.
Proportions of classrooms vary with kind and arrangement of desks. A long narrow room should be avoided, while a room approximately square is most satisfactory.