Been teaching tandeming since 1975.
Taught well over a hundred couples. 99% like it.
Explain to both how to mount/hold the tandem. Communication is key. Teach what the key words are. What to do and not to do (stoker do NOT do the hula back there and do NOT try to steer!).
After you explain all that, take the prospective captain for a quick spin as stoker.
I've just told 'em how to communicate but . . . within the first 100 feet I shift, jam the brakes, swerve without saying a word.
The new prospective captain is of course startled. But I say "this is what it feels like when you do NOT communicate with your stoker. Now, let's communicate properly."
When I take the prospective stoker out, I'm super attentive, communicate properly and all's well.
Then after that, let the prospective captain take the bike out solo so he can get the feel/handling of the long bike.
After that, the prospective captain takes me for a ride as stoker and I critique what he did right/wrong. I usually stand up on the pedals and stomp on it to show what that feels like.
Only after all that do I let the couple get on the bike together.
We do offer the use of a hatpin to stoker to use on captain if he screws up . . . it works!
Explain to them that is a bit of learning curve, but things will keep getting better/easier.
Pedal on TWOgether!
Ryudy and Kay/zonatandem