Not whether to pack your child's lunch box with Jamie Oliver-approved food or stuff in some crisps, but what to wear at the gates.
In one corner are the yummy mummies – the full make-up and blow-dried hair brigade.
In the other are the so-called 'slummies' who favour a more low-key approach and have been posting on the Mumsnet chat forums.
A handful of celebrity mothers joined the fray, treading a fine line between both camps this week.
Dropping off her boys, Arpad, 11, and six-year-old Aurelius at their exclusive London academy, Elle Macpherson seemed at first glance to be taking the casual route with a sensible jeans-and-flats ensemble.
But check out the details - her statement bag and belt showed she'd clearly thought about her oufit.
Stella McCartney's school run combo was comfortable, while still displaying her credentials as one of the world's leading designers.
Her slouchy dress was in the nautical blue and white palette that dominated catwalks recently. Then there were the bang-on-trend shoe boots.
Meanwhile, over in Spain, accompanying her youngest, two-year-old Sofia to her first day of nursery, Crown Princess Letizia, was the epitome of dressed-down European chic.