I recently bought 'NATIONAL GEOGRAPHIC Gross Science Lab - 45 Gross Science Experiments for Kids, Dissect a Brain, Burst Blood Cells & More, STEM Science Kit for Kids Who Love Gross Experiments (Amazon Exclusive) Super Gross Science' link and I'm floored by how great it is! I'd heard good things about National Geographic's science kits but when my nephew got his hands on this one we were both totally blown away.
It comes with all the supplies needed to do 15 super gross experiments and 30 more that use common household items - perfect for kids who love gross stuff! Exceptionally detailed instructions illustrate each step so you don't have to worry if your middle schooler can figure out how to mix the chemicals or whatever (which I was). In addition to the fun of doing icky experiments it also teaches kids about polymers reactions, pH levels and other scientific processes in a way that's actually enjoyable rather than boring lectures from some old professor with a tweed jacket! Win win.
My family was even joking around the lab table doing something they like calling ‘gross panini requests', asking each other “can you make me five eyes floating in slime please?!", which only goes to show just how much everyone loves pulling apart brains and making boogers boil like mad scientists :) All in all we highly recommend this awesome set — great fun AND educational value!!