I found a relative at what seems to be a boarding school, in the 1851 census. The reference is HO107, piece 2509, fol 439, page 21.
The dwelling is named as Pen-ddol, parish of Trevor Uchef, near Llangollen, where Mrs Matthews, a widow, has two young daughters and her two sisters as teachers. The pupils are three girls, one aged 11, two were 13 and two boys, one 11 and my chap (whose family were mainly in Lancashire) only 5.
This seems an unlikely spread of ages, and I wonder if anyone with local knowledge could offer more information about this establishment.
Thank you