Reddit mentions of Elenco Electronic Playground 50-in-One

Arduino and Rasberry Pi are two embedded system ecosystems that have big communities and support. You could get a newb kit and start from there.

Also, back in the day, it used to be all about analog electronics. I had the "Getting Started in Electronics" Radio Shack book by Forrest Mimms, and a 50-in-1 experiment board.. Super fun.

If I wanted to make something computer-y / motor-y, I would probably make a track-running inverted pendulum to freak out the squares...

It looks like you're set up as far as it goes for electronics (projectors, a TV, and hopefully at least one computer) so I wouldn't waste any money there. Look for things that are reusable and don't have a high cost of upkeep.

Basics

First and foremost set aside some money for classroom basics that will be useful for any type of science lab.

• Safety goggles
  
• Good quality rulers
  
• Tape measures
  
• Stopwatches
  
• Duct tape
  
• Wire clips
  
• Cheap multimeters
  
• Battery chargers
  
  Life Sciences
  
  This is probably the cheapest subject to teach since a lot of the things you'll cover can be grown in coffee cans and mason jars. You'll need flower pots, some spades, watering cans, and some grow lights if you don't have good natural lighting. You can do simple and cheap projects like a tabletop biosphere with some mason jars. You should probably get one decent microscope with a camera you can hook up to a computer or directly to a projector. The students don't need to learn to use a microscope, they need to learn about whatever you're looking at with the microscope.
  
  Physical Sciences
  
  If you want to teach the kids electronics buy this whole series of books and several of these bad boys. The Electronic Playgrounds are fantastic for teaching basic electronics because they don't need any soldering, are very versatile, and best of all reusable. If you lose some of the wire they come with just clip your own. IIRC the instruction booklet gives all the gauges different wires.
  
  Earth/Space Sciences
  
  These sciences are larger in scale and scope than you might be able to demonstrate in the classroom. You might buy a cheap weather station and make a project out of keeping track of the readings. Over the years students will be able to compare their measurements to those of classes made years prior. This is also a place where decent software or just some good imagery will help teach the subject.
  
  Check out the following sites for some idea for experiments/demonstrations/activities and then work backwards from there. Figure out what you would need to perform experiments you think will fit your lesson plans and then build a shopping list. There's a multitude of science demonstration projects you can do very inexpensively. If you're smart with your money you can fund your science lab for the next few years even if you've got to spend all the money right now.
  
  Exploratorium Science Explorer
  PBS Kids Science Experiments
  Hands-on Activities for Teaching Biology to High School or Middle School Students
  National Geographic Lesson Plans
  Scientific American Bring Science Home
  
  
  Get a class subscription to Make magazine, National Geographic, Astronomy Magazine and whatever else seems appropriate. Build a small science library in the classroom. Get some good science oriented DVDs. As a practical matter you might also want to get a nice locking cabinet to store whatever nice new things you end up buying. It would be horrible to spend your grant money only to have all your new expensive equipment stolen by some asshole.

First of all props to you to introduce your son to electronics and ask to find a good method for him to learn it out of interest.

I remember having electronics kits which had a bunch of simple components connected by those metal spring terminals. They often came with booklets to go step by step through simple projects to gain some understanding.

Perhaps you could look at toy shops and see if they carry some educational electronics kits? I remember book shops also sold them though I'm not sure if they'd still.

I found this on Amazon, seems a bit different with magnets snapping together but looks like it goes step by step in explaining: https://www.amazon.com/Snap-Circuits-SC-300-Electronics-Discovery/dp/B0000683A4/. Looks a bit expensive but not sure if that's different in the US.

Oh boy I even found one of those kits with the spring terminals: https://www.amazon.com/gp/product/B00000IUD2

Best of luck!

This is similar (although not as good)

https://www.amazon.co.uk/Elenco-EP-50-Electronic-Playground/dp/B00000IUD2/ref=sr_1_10?keywords=electronics+kit&qid=1556184856&s=gateway&sr=8-10

http://www.amazon.com/Elenco-Electronic-Playground-Learning-Center/dp/B0035XSZDI/ref=sr_1_1?ie=UTF8&qid=1412479994&sr=8-1&keywords=Electronic+kit

http://www.amazon.com/Elenco-Electronics-Snap-Circuits-Snaptricity/dp/B0013BL3LK/ref=sr_1_38?ie=UTF8&qid=1412480035&sr=8-38&keywords=Electronic+kit

http://www.amazon.com/Elenco-EP-50-Electronic-Playground-50-in-one/dp/B00000IUD2/ref=pd_sim_t_5?ie=UTF8&refRID=0KPKE2ZHBDF256TN2M8K

http://www.amazon.com/Elenco-EP-50-Electronic-Playground-50-in-one/dp/B00000IUD2/ref=pd_sim_t_5?ie=UTF8&refRID=0KPKE2ZHBDF256TN2M8K

I had the Electronic Playground thing back when I was a kid. It was a lot of fun and I learned a lot from it.

They still do similar toys, but without the multimeter, function gen etc. I had one when I was a lad:
https://www.amazon.co.uk/Elenco-EP-50-Electronic-Playground/dp/B00000IUD2/ref=sr_1_1?s=kids&ie=UTF8&qid=1523449652&sr=1-1&keywords=learn+electronics