Martha from Argyll, Scotland, began posting her lunch pics this week. She's now had more than 100,000 visitors and press attention from across the world.
Celeb chef Jamie Oliver even tweeted: "Shocking but inspirational blog. Keep going, big love from Jamie x."
The first pic (top) of her daily Â£2 lunch featured a pizza slice, a croquette, sweetcorn and a cupcake.
Martha wrote: "I'm a growing kid and I need to concentrate all afternoon and I can't do it on one croquette. Do any of you think you could?"
But Martha never set out to be a healthy food campaigner - her NeverSeconds blog started as a writing project with her dad Dave.
They decided on school dinners because it was a subject she could write about every day.
She gives each meal a 'food-o-meter' and health rating. She also counts the number of mouthfuls it takes for her to eat!
As well as improving her writing, Martha revealed: "The good thing about this blog is dad understands why I am hungry when I get home."
An Argyll and Bute Council spokesperson said: "Our school meal provision is fully compliant with nationally agreed nutritional standards.
"Young people make a choice from at least two meals and salad, vegetable, yoghurt and cheese options are available each day."
A nine-year-old girl's blog showing photos of her school dinners has become an unexpected internet hit!