If you have an auditioned choir your will have sorted much of the differences in musical abilities through that process. If you have a volunteer, non-auditioned community choir, you will get varying degrees of musical knowledge and ability in each member. No matter which type of choir you have, and no matter what ages you have, you will still find differences. As the music director or choir leader, you must be able to balance those abilities helping each one to continue on their personal learning curve.
If you "dumb down" your work to accommodate those who have not much more than a wish to sing, you risk losing the interest of the more adept members. The opposite will also be true. How do we balance our music selections and teaching process so that each person learns and enjoys the experience? Here are some of my suggestions.
1. Start by singing. At first, you really can't plan for a diverse group. My suggestion is that you first sing some partner songs even as simple as Frère Jacques and Row, Row, Row Your Boat to see how they handle the singing of different sounds around them. In a way, this is a group audition. You can also do rounds which allow you to see how independent each singer seems to feel. Watch their faces as well as listening to the sound. You will see their frustration or security. Now, ask them how they felt as they sang.
2. Hand out some music. I like to start with an S.A.B. piece for adults. Inevitably, you will have someone who can sing soprano and someone who is fairly adept at alto. If you put the men together singing baritone to start, you are sure to have someone in there who will be able to read at least part of the piece. It is even better if you can find a piece that has verses and chorus. Even if it is all written in 3 parts, you can decide to sing a verse in unison. That helps the less proficient readers to feel as if they have achieved at least that part. Then, ask them how they made out as they sang.
3. Break out to practice the parts if you can. This may take a couple of practices to achieve as you will want to find out if there is someone who is capable of taking the ladies or the men off to go over those parts separately. This builds confidence and helps speed up the learning. In smaller groups, it is easier to address individuality. When they come back together, sing! Then, ask them how they enjoyed the separate practice.
4. Don't beat a dead horse. When you have done the above, and the singers are still struggling, reassess. If they are having trouble with the pieces you have chosen, you might have to consider something less challenging until they build confidence. Whatever you do, don't keep working at a piece that causes continuous struggle. We will sometimes practise a piece, put it away and pull it out months later and amazingly, it works. If it is dead, let it lie. Ask the choir what they think about your decision to let it drop.
5. Ask them how they are doing. Keep your choir as an active part of the process. Are they feeling good about their progress? What do they suggest could be changed or continued? There are few situations that can't be solved by talking about it. Really. They know best how they feel. Those who would rather not talk in a group will be happy to chat quietly at the end one to one. I firmly believe if you communicate and remain open to how they feel, you will understand your singers and be much happier with the results. You will sing music that challenges and do it well with everyone feeling a sense of accomplishment.