When I was at school, the midday meal was 'dinner' rather than lunch on schooldays. 'School dinners' is a common phrase, but I've never heard 'school lunches'. At home though, especially on Sundays, the midday meal would be lunch (as in 'Sunday lunch' or 'BBC Lunchtime News').

Tea is a mid to late afternoon light meal. Supper is a late night light meal or snack.

I don't always have a 'main' meal, but if I do it's more likely to be in the evening.