STEM and Educational Resources

Stem Activities from Discount School Supplies
STEAMsational
Planet Smarty Pants
Little Bins for Little Hands
Ask Dr. Universe
Exploratorium
How Stuff Works
STEMWorks
Funology

Science

Oil spill activity - This one, along with many others, are from a list featured in the article 11 Simple STEM Activities for Kids That Will Stimulate Young Minds by Megan Ruesink.
The Incredible Shrinking Bag and the Crushed Soda Can – These two garbage science projects from Teach Beside Me take a potato chip bag and a can of soda and turn them into some pretty cool science experiments that are great for elementary aged kids!
Frog Study – You can tailor this activity to kids in preschool all the way up to high school. Brought to you by Harrington Harmonies, this amphibian activity will teach students about observation, life cycles, and life science.
Water Cycle in a Bag – This is a great activity you can find on From Playdough to Plato. It all takes place in a tiny little Ziploc bag. Tiny Dancers, Build a Volcano, Apple Oxidation
Science Spot - Science projects that can be completed with or without Internet access
The Happy Scientist - Just explore, have fun, and learn some science along the way.
Climate Kids - This NASA initiative covers a wide range of topics including weather, climate, atmosphere, water, energy, plants, and animals.
STEAMsational-Science Experiments for kids

Technology

Squishy Circuits - This activity from STEAMsational involves conducting electricity using two different types of "dough."
Become a LEGO Mechanic – Homegrown Learners provides some great videos and detailed explanations of how to use LEGO to teach elementary and middle-school aged children about technology, engineering, math, and building.
Create a Stop Motion Animation – This is a great project to teach beginners about the filmmaking process, whether in elementary or high school. It involves a little bit of storytelling, experimentation, problem-solving, and hands-on technology. The easy-to-follow instructions to create a stop motion video are provided by TinkerLab.
Coding For Kids Activities

Engineering

Bridge Building Challenge – Using just some glue, craft sticks, a ruler, and some parchment paper, kids can build a bridge and test just how well it will hold up. Busy Kids, Happy Mom provides this bridge building tutorial that can be applied in the classroom or at home.
Build a Catapult – The Kids Activities Blog provides this fun and easy engineering activity using just a few simple craft items. What kid isn’t going to enjoy learning about engineering by launching objects across the room?
Up, Up, and Away – This activity from The Homeschool Scientist gets kids working on building their own custom aircraft.
Propeller Car – Instructables has dozens of great engineering projects for all ages that re fun and simple. This one is about designing a propeller-powered car.
Miniature Robot – Want to show kids how to make their own customizable battery-powered robot? This easy and fun tutorial from Red Ted Art will get them up and running in no time.
Kids Think Design - Explores careers in fashion design, graphic design, interior design, book design, product design, film and theatre, architecture, animation, and environmental design.
Build a Rubberband Helicopter 
The Cork Launcher 
Build a Simple Pneumatic Machine 

Mathematics

Early Math Lessons – These simple math lessons are great for younger children to teach the very basics of math. Our Journey Westward brings us these math ideas to teach division and logic.
Go on a Math Hunt – This is another great activity for making math fun. Raising Lifelong Learners brings us this idea for a math hunt that’s great for elementary-aged kids who are homeschooled.
Nerf Gun Math – This fun outdoor activity for teaching basic math is geared towards older elementary-aged children. No Time For Flash Cards breaks down the instructions and materials needed to create this simple Nerf Gun Math game.
It’s About Time – Check out these activities from Education World that are all about teaching how to tell time.
Bed Time Math - Math as a fun part of your daily family routine
Instructables - 3D printing projects and Coding projects, involving math and other K-12 subjects
Math -Dreambox
Phonics-Numberblocks
Money Math 
Mirror Symmetry