As a teacher, how do I convince my school leaders that having teachers teach several subjects is a terrible idea?
Adam Smith thought a lot about this type of thing in the 1770's. He figured in The Wealth of Nations:
It is not from the benevolence of the [school leaders], butcher, the brewer, or the baker that we expect our dinner, but from their regard to their own interest.
We address ourselves, not to their humanity but to their self-love, and never talk to them of our own necessities but of their advantages.
Most leaders-school or otherwise-want to give you whatever it is that you need to succeed.
You may, however, want to figure out how to make it easy for them to give it to you!
In more practical terms, that means:
1) Identify their their worries. (Or "interests" as Mr. Smith might say.) What are their biggest, strategic priorities? (Improving student growth & achievement by x, etc.)
2) Align your proposed solution to their worries. How will your suggested change address their concerns? (My strategy will help us improve student growth and achievement by... according to... sources: Perhaps there is a nearby school, etc. that is otherwise similar except they implement your solution and have better scores, etc.?)
3) Impact Analysis & Cost/Benefit. How do you illustrate/help them best understand the impact this change will have relative to other areas/decisions they might make? (Leaders always have multiple demands for their attention/time/decision-making... How do you make the cost/benefit easier for them when weighing what changes to make and how?)
4) Anticipate & Provide Other Relevant Data/Facts. Thorough leaders will want to know things like whether is the change permitted within policy or will I need to connect with legal/my supervisor, etc. They will want to know how many other people the said solution might impact... and how many of said people will be upset/happy with the change. (This means staff, other students, and possibly parents in this case!)
It would help to know more about your situation. Are you currently teaching multiple subjects and trying to focus on one or two, or are you currently teaching a few subjects and the school wants you to teach more?
A major disadvantage to teaching outside your training and abilities is imparting incorrect information to students. I have seen students who learned Spanish with a French accent from the French teacher, teachers giving students wrong instruction in math, and an elementary school teacher giving students the wrong way to spell "snail" ("snell"). I would hope we would not expect someone who is colorblind to run the art program or someone who is tone deaf to run the music program. Teaching in an area where you are very poorly qualified can lead to imparting incorrect information.
Teaching too many subjects will make it hard for you to focus. If you spend the same amount of time developing lesson plans for 6 classes as for 3 classes, you automatically have an average of half as much time to prepare for each class.
Teaching multiple subjects with a discipline area (i.e. math or science or reading/writing) can be beneficial. You can make connections as a teacher, and help your students make connections.
I can't say teaching several subjects is universally a terrible idea; I would need to know more about the specific situation to judge whether its a good or bad idea.
Quite obviously you feel that knowing a subject matter is more important than knowing kids and how to teach them. My 1st job was in a one room school, and I hot only taught all subject areas, but also grades K,1,2,3,4,5,&7. I also taught 15 years in laboratory schools at 5th grade level before I was appointed Coordinator of Innovation and Experimentation in Education. Near my last year of teaching at the university, I arranged an exchange and taught in a modern open plan, depressed area school to become aware of the changes in child development. I see no educational advantage to a concentration in a subject matter over the opportunity to know children.
In California, being assigned to teach outside your credential is illegal. Simply inform them that your credential does not allow you to be given the assignment the administrator wishes you to take. Then have the Association file suit in its own name on this issue. We did!
There are many studies about this issue, and they all say the same thing. This is not a good idea. It predicts bad outcomes for learning.
This does not apply to the elementary school where teaching all subjects is traded for teacing the same only one class of students each day for an entire school year.
Good question, and I agree with you that teaching 7 subjects is a TERRIBLE idea. I think it's one of those "that's the way it's always been" arguments. While I am a strong supporter of public school, I also think there's room for improvement. Things change-KIDS change. It makes much more sense to me for each teacher to focus on one or 2 curricular area and teach them really well.
I dont have the answer to your question, sorry. It's a great idea though.