I'd have to agree with the others, it sounds like it was too much for him. Well, this is assuming he's a treat kind of dog. I know Miko isn't, so teaching him agility was hard when his "treat" was to chase down a toy (i.e. with food, you can kinda lure them if needed). If he is a treat type of dog, then it's too much. Time to go back to square one. I can find out how my trainers taught Koji to be okay with the movement. I know she didn't work too much with a buja board. But then, Koji is massively food motivated. So all I needed was some great treats (at that point, I had to use hot dogs).
Don't get discouraged. It took Koji a lot of private lessons to get the teeter. Heck, took him a month of private lessons (about 4-5) to get the tunnel and love it. And when I mean private lessons, I mean that my trainer worked with him alone for 30 mins (I wasn't there). So, think of how much that time is for us non-trainers. Yikes.
The person who wrote about how you know when it's time to quit, I think that's a good point. The reason I didn't stop was because Koji loved to run and do jumps and tunnels. I worked slowly with everything else, and now he seems to love it all (okay, jumps more than anything else). I think you can tell if your dog dislikes agility. I can say that Miko did agility FOR ME. He wasn't that into it, but wanted to please me, so he did it. It's one reason I didn't continue it. His joy was catching balls/frisbees, definitely not obedience nor agility.
And lastly, don't forget you always have NADAC if Shadow never gets the teeter. Also, in CPE Level 1, they don't have the teeter. You have options if you want to trial. Just not USDAA, AKC, or higher levels of CPE. NADAC is a good choice considering where you live, so again, check it out if you want to compete before the teeter is solid.
p.s. I love when dogs finally get things and want to show you. It's so adorably fun to watch!!