Wigan Album

Keith, I once owned a couple of houses in Loch Street and Cross Street, Orrell. There was a small communal, enclosed area behind the houses with an entrance 'ginnel', it was where the bins and washing lines were for 4 or 5 houses.
An old lady, who lived nearby, called it "t'dryin' yard".
I wouldn't have imagined a school having the same set-up there, on Parson's Walk, but who knows?

Thank you James for that interesting input. As usual I should have consulted that everyday reference these days, namely the internet. Here is one interpretation "Bleaching and drying both used to be mainly outdoor activities, and they were closely related. The stretch of grass set aside for these jobs was called a bleaching-green or drying-ground. Whether you were spreading off-white linen on the ground to bleach in the sun, or just putting your laundry there to dry, or if you were hanging it on a breezy line” Now, as you say, who knows? If that was its purpose who would be using it, there does not appear to be any industrial activity nearby and if so would they use it in such close proximity to a school playground?

Ref. the drying ground - when the map was made, did Wigan Grammar School accept boarders?
If it did, it is likely there would have been a laundry, hence the drying ground.
All around this time, UpHolland Grammar School, only four miles away, had about thirty boarders, so this may also have been the case at Wigan.

Ray, thank you for that possibility, it certainly sounds very plausible, not something I had ever given consideration to.

Based on a SEARCH: Drying Ground reference was likely associated with Outdoor drying and bleaching.
Bleaching and drying both used to be mainly outdoor activities, and they were closely related. The stretch of grass set aside for these jobs was called a bleaching-green or drying-ground. Whether you were spreading off-white linen on the ground to bleach in the sun, or just putting your laundry there to dry, or if you were hanging it on a breezy line, you wanted a flat sunny area for this.