It shows a PE lesson (also known as physical instruction/education/training/fitness).
The picture is captioned:
(1.) - CRAWFORD STREET BOARD SCHOOL, S.W.
Commencing positions of the upper and lower limbs.
(This school is still in existence today: it is now called Crawford Primary School, and is a member of the Gypsy Hill Federation.)
This photograph is part of a series of activity sheets, showing lessons in various British schools, in Edwardian times.
I am not sure of the history of the pictures.
They look as if they were originally in some sort of album or folder.
Perhaps they were from a teachers' manual or similar?
The photograph measures around 4.75" x 3" (12 cm x 7.5 cm) , which is slightly smaller than postcard size.
It is printed on a plain sheet of paper, around (the sort that was commonly used for "book plates" in Edwardian times).
This sheet is about 12.5" x 7.75" (32 cm x 20 cm) . It has been cut (rather unevenly) along one side, presumably when it was removed from its original album or folder.