I do remember the transition at around 13 when the lined flannel short trousers were replaced by the long ‘terylene?’ trousers of which I feel sure I was very proud. However, there were no back pockets and the material quickly became shiny and very visibly thin, added to which, they fitted more and more snugly with time. The application of cane or slipper was of course much more effective, but I am not sure we thought about that change of dress.
I think in my day we still wore trousers that were at least a natural fibre/ synthetic mix which often had back pockets. These were usually checked before canings and emptied as necessary.