Our thanks to a number of people for pointing us towards this. So, which gender was the head teacher primarily thinking of, when she issued her note to ‘parents’? Maybe there’s a small clue in the final sentence in the article:

In another incident, Joe McGuiness, head of St Matthew’s primary in Belfast, wrote a similar letter to parents saying as many as 50 mothers would regularly turn up at the school gates in pyjamas and slippers.