Sorry, will be long! DS is 9. For the last year or two we have struggled to get him to eat his packed lunches. It started with most of his sandwiches being left, then his yoghurt, sometimes crisps too. Sometimes he'd eat nothing. I've tried everything - no "snack items", wraps, salads, crackers and cheese, pasta/rice salads, quiche, pizzas made from rolled up pasty, school dinners. We've planned meals of his choosing at the weekend and he's helped make them. Still the same, he doesn't eat enough to keep a mouse going 
I think the problem is that he wants to get out as quickly as possible. He can be the same at home if there's something he'd rather be doing, usually playing football! The problem is that he's borderline underweight for his age and I'm concerned. We have seen some improvements at home; I've tried smaller portions so that clearing his plate becomes manageable, I involve him with planning and cooking where I can. We make meal times family time to distract him from whatever else he's itching to get back to. He's not at all a fussy eater and he does enjoy food when he concentrates on eating it!
Due to his weight concerns I've asked whether school (tiny village school, less than 100 pupils) could keep an eye on him at lunch times and encourage him to eat/not let him out until he's at least eaten something. They said it's not their job to force him to eat, if he was hungry he'd eat and that's that. Due to wrap around childcare he sometimes goes almost 10 hours without food so I'm at my wits end and desperate for advice! Should I expect more help from school?