Sheesh, nobody is writing anything but "George Romero zombies" anymore. It was creative when Romero did it originally, but now it's just derivative. I'm getting really bored with all the zombie armies raised by cosmic rays, or hazardous waste, or germs, and going on a rampage for brains, turning anyone they bite into another zombie. Jim Butcher was a lot closer to the original zombie lore with the dead being raised by necromantic sorcery, and under control of the one who raised them. For a change, I'd like to see the old traditional zombies, being raised by a bokor using invocations to Damballah. They didn't eat brains, either. In fact, traditionally, if they ate meat or salt it would break the bokor's hold on them. In Haiti, where they were supposedly used as field slaves, they were alive enough to need to be fed, and given a diet of unsalted cornmeal gruel.
I totally get your sentiment and when I mentioned Romero it was ment only in reference to how the characters and zombies were introduced into the story.
I agree it would be cool to see zombies like you mention but I don't know if that could fit into the OP's storyline of kids trapped in a school surrounded by zombies, but then again I'm not sure of the direction of the story so maybe it could.