I'm sorry but all this techno babble you are so willing to shove down... I mean impart to them is not why they are there. I teach many seniors and for a while tried to get them to understand but the reality is they just want to take better photos. I believe you should revamp your whole system to cover composition and lighting. This they can understand and will improve their results. Have them assess the light of a scene and then determine where to shoot to achieve a good result. Show them back, side and front lighting and try to get them to "look" at the light and not the cute subject. Show them the rule of thirds and all the varieties of it. When to choose landscape and when to choose portrait format. Lines, shapes, contrast and framing will all allow them to advance their skill level. Give them a small challenge each week/month whatever the time frame is and they will all revel in trying to achieve the goal. In time, some will try and comprehend the techno babble and you can then advance their knowledge. The rest just don't care about that aspect, they just want to have fun.

Well, since I am not a good photographer and do not claim to be anything more than an artist, what I have to say about this is not important and I'm sure will matter to no one at all, but being one of those seniors between the ages of 80 and 90, I think I know what will be fun for them and what will bore them to the point of wishing they were somewhere else. I not only FEEL what they feel, but I sometimes teach seniors to paint at Sr. Citizens Centers and Senior Sunday School classes at Churches. I show them they CAN do it and they are thrilled to see what they have done when it's over. Their attention span is not as long as middle aged people, so holding their attention long enough to learn much is not easy. Keep it simple. Teach them about the importance of good lighting first, then teach them simple stuff, like, not to have trees or poles coming out of heads or backs and make it FUN. Teach them when to fill the frame with a subject and when to back way off. Keep the wording simple, not words they will have to ask about. It's doubtful that they are out to sell photos. Just keep foremost in your mind that they want to have FUN making better pictures, not necessarily masterpieces. I'm sure that what I have said may do nothing for anyone but those seniors who are about to either have a great time or......

I also teach basic digital photography and my view is you are over complicating this, especially for that age group.. The point I try to drive home is that each full f stop let's in twice or half as much light and I depict this with an image of aperture openings of full fstops ranging from F1.4 to f22 or so the image is of the various diaphragm openings. I then talk generally about the depth of field aspects of f stops and focal lengths without getting into the math. Finally I refer to available phone apps that will provide dof values for various focal lengths and apertures. It seems to satisfy my students which run in age from low 20 - 75 or so.

When I have explained the exposure triangle I usually start out in very general terms and then gradually flesh out the settings with specifics once the concepts are clear.

For example - I would generally start out defining what we mean by "exposure" - very simple terms - how light or dark the photo is - too much exposure the photo is way too light and washed out - too little exposure the photo is way too dark and muddy looking - somewhere in between we find the "correct" exposure where the photo appears the way we want it to appear.

Next - more light into the camera results in more exposure and a lighter photo - cut back on that light getting into the camera and the photo is rendered darker.

What are the controls on the camera that regulated how much light gets into the camera?
1. Lens aperture - which is a measure of the size of the opening in the lens - bigger opening allows more light into the camera - compare to a round window on a ship (porthole) - bigger window, more light - smaller window, less light
2. how long we allow light to enter the camera - longer period of time, more light enters - lesser period of time, less light enters
Combo of the two determines how much light overall can enter.

How sensitive is the camera (or more specifically the CCD or CMOS sensor) to light - introduce concept of ISO as a measure of how sensitive the camera will be to the light entering the camera.

So far - no numbers or mathematical ideas used at all.

Once the basic concepts are clear - introduce the idea that the end result on exposure is a combination of the factors just introduced. I have found that a useful (as well as very easy to draw) diagram is as follows:

Draw three vertical lines side by side - label the three as ISO, Aperture, Time (Shutter Speed)
Draw about a half dozen hash marks to divide each vertical line into segments (make sure the hash marks all line up and are equally spaced
Indicate that as we move upward on any of these lines the photo will get lighter and when we move downward the photo gets darker
Now define each hash mark as a doubling of light for each hash mark in the upward direction or a halving for each notch downward.
Put a check mark next to one hash mark on each line (somewhere around the middle in each case) and ask the class to assume that this combo is the "correct" exposure
Now point out that a move up on any one will result in a lighter photo and a move down will darken the photo
Next concept - if we move up one of the factors by say 3 notches (leaving the others alone) the photo will get much lighter (and probably washed out) - We can correct for the now too light photo by moving either of the other two factors (or both in combo) a total of 3 notches down to achieve the same exposure as we originally had - just a different combo of the 3 factors. (Note: I often compare this to using a wall mounted dimmer switch some of which you slide up or down to change the light.)
Now flesh out the diagram with the numbers - Highest ISO, Widest Aperture and Slowest Shutter Speed at the top of each vertical line.
The "math" is really pretty simple and intuitive for ISO as well as shutter speed
For aperture - seems counter-intuitive so you will need to point out that the aperture settings are actually in the form of fractions - the top number is represented by "f" and does not vary unless you use a different focal length - so as the bottom number gets larger the value of the fraction gets smaller (as in smaller diameter lens opening letting in less light) - make the concept simple by using the slicing of a pie as an illustration - the whole pie is "1" in the numerator - as we cut the pie into more pieces (4 pieces, versus 6 pieces, versus 8 pieces) the size of the pieces get smaller.
Last concept - there are many combos of aperture, shutter speed and ISO that will give us the same "exposure" but not really an identical photo - this is where you explain how aperture effects depth of field, how shutter speed impacts motion (or lack thereof) in the photo - subject movement and/or camera movement implications, and how ISO effects overall image quality (noise, etc.)
Anyhow - hope this is helpful to you.

Create an in depth Instructors lesson plan, this should anticipate any questions that the students may have. Practice your presentation before giving it to your class, fine tune it with each presentation you give from the questions that you are asked. Your presentation should be smooth flowing and answer any questions before they are asked. If you are asked a question and don't know the answer, your response should be I don't know but will get an answer for you, and make sure your follow up with them. Be truthful with them.

Here is an example: I work for a major airline and in 2002 our engineering dept started looking at computer software for our maintenance documents for the technicians. They went to our in house education department and asked them to create a class, the ed department told them it would take a min. of 18 months to create a class. Engineering then asked if any of the DST (Designated Station Trainers) could develop a class and how long it would take. I was the second one to take up the challenge after the first one quit his job. I gave them a time frame of 30 days and that I would need complete and full access to the program. I had a workable lesson plan with training aids and hand outs within 20 days, however engineering was not ready to roll out the program to the people that would be using it. I took that time to keep refining the instructors manual, training aids, handouts and exercise book. My final product was The instructors manual was 400+ pages, The students manual was 200 pages and the exercise booklet had 20 exercises in it covering everything from the most basic to and in depth exercise that would be above what they would be authorized to do. What was unique about this is that I was the author of the training materials, the instructor and the tech support. I was the only instructor from 2002 to 2013 and it got to the point that engineering was coming to be for help. I was so familiar with the program that I could answer questions in my sleep and this did happen on a couple of occasions. And their were times that I did not have a solution right away and had to work on it.

Here is how I would approach this class:

Find out what the students are interested in doing ie snapshots, landscape, wildlife, portraits, etc
Decide on how much time you want to spend on teaching; i.e 1 hour, 1 day, 1 week, a month etc.
Keep it simple
Keep the class time short. Do multiple sessions if necessary. Short class times keeps the interest level up
Have training aids for use in the class. Develop your own. This will be based on what they are wanting to learn
Have handouts for the students that will cover the topic in a condensed format/version
Develop exercise that would cover at least one of the topic in that days class session. This is like a homework assignment.
Have the students bring copies to the next class for critique. Pick the worst, the best and in between as examples of what to do and not do. Do not spend a lot of time on this before going into the next subject matter.
Have a period for questions and answer, or let them know that you will answer questions through out the class session or after class
Be willing to help them with any difficulties that they are having
Most of all go out there and have fun photographing the world as they see it

I hope this helps. Teaching a class is not as simple as people assume it to be, it takes a lot of prep work before getting into the classroom

Well, since I am not a good photographer and do not claim to be anything more than an artist, what I have to say about this is not important and I'm sure will matter to no one at all, but being one of those seniors between the ages of 80 and 90, I think I know what will be fun for them and what will bore them to the point of wishing they were somewhere else. I not only FEEL what they feel, but I sometimes teach seniors to paint at Sr. Citizens Centers and Senior Sunday School classes at Churches. I show them they CAN do it and they are thrilled to see what they have done when it's over. Their attention span is not as long as middle aged people, so holding their attention long enough to learn much is not easy. Keep it simple. Teach them about the importance of good lighting first, then teach them simple stuff, like, not to have trees or poles coming out of heads or backs and make it FUN. Teach them when to fill the frame with a subject and when to back way off. Keep the wording simple, not words they will have to ask about. It's doubtful that they are out to sell photos. Just keep foremost in your mind that they want to have FUN making better pictures, not necessarily masterpieces. I'm sure that what I have said may do nothing for anyone but those seniors who are about to either have a great time or......