You can't really make a comparison between then and now.
Firstly, if Priscus's primary school was in Wigan, it's obvious that there wouldn't be many miners' kids amongst the pupils as there wasn't many miners lived in Wigan.
Ask the same question in Haydock, Golborne or Leigh and the answers would be totally different.
Today, most Wigan workers (and I suppose you mean anybody under Wigan Council, not Wigan?) travel out of the area both to work and to spend their wages.
Back in the day, most people living in 'Wigan' would work in Wigan and spend their money in Wigan too, in local shops for local people, owned by the parents of some of the kids in Priscus's class!