Hmm, my instinct when I first heard about this was pretty much the same as the OP's i.e. how very dare he? But my understanding is this affects girls in Yrs 7-10 i.e. 12-15 year old children. Just reading through the "let girls be girls" MN campaign, I tend to think that this falls under the same remit i.e. children are feeling pressurised to dress in a sexualised way.
From the campaign:
â—¦In 2007, a study by the American Psychological Association found that: "Sexualisation has negative effects in a variety of domains, including physical and mental health, and healthy sexual development." Possible ongoing effects identified by the research include: low self-esteem, poor academic performance, depression, and eating disorders such as anorexia. The report also warned that sexualisation may contribute to the prevalence of paedophilia.
â—¦A 2008 study by Girlguiding UK and the Mental Health Foundation found that premature sexualisation and pressure to grow up too quickly are two "key influences" in the anxiety felt by girls.
â—¦The Mental Health Foundation said: "Girls and young women are being forced to grow up at an unnatural pace in a society that we, as adults, have created and it's damaging their emotional well-being. We are creating a generation under stress."
So isn't the Head Teacher doing what we are asking retailers to do? Or am I missing something?