My DD almost thirteen has been skipping lunch at school and it's driving me crazy.
She comes to meet me after school for a lift home every day and asks for food/money, when I question her she has a terrible stomach ache and skipped lunch and just ate other people's leftovers!
At home she eats breakfast and all her dinner, snacks if she's hungry so it's not an eating disorder level but from breakfast to dinner she hardly eats much, what she would eat would just be things like crisps at school 
I put money on the dinner card and my house has PLENTY of food at home usually, that she is welcome to take. I have made things she just leaves in her bag and forgets
IMO she looks peaky and took ages to get over a recent cold. I'm fuming that she takes food from others, can't be bothered to walk to the canteen or get food from home and gets to the stage of agonising stomach cramps/acid indigestion from being starving. She's not poor or neglected but if school saw this they may think she has no money or access to food!
Tonight I gave her a huge lecture about looking after your body, the harm it could cause (headaches dizzy spells, fainting, long term issues) and told her categorically that she would eat something of substance at lunch either from home or the canteen.
I'm not sure she's listening. She's eaten her dinner but why be so lazy you would rather risk having a horrible stomach ache than walk a few yards to buy bloody food?! Why am I so mad about this?'