At primary school age, it would have been anything extremely weather inappropriate. Saying that, when they got to the annoyingly irrational 'don't want to wear a coat' stage in Y6 I just thought, well be cold then!
Beyond that, I've never said it. I've never commented on my daughters outfits, and I never let her dad say anything either. She's now early 20's and yes, sometimes wears revealing clothing, but as often as not, is happy to go out in a hoodie and jeans without a scrap of make up.