It's an inescapable fact of education that what we do as teachers today affects the work of other teachers later in a student's life. That means we inherit strengths a good teacher built, which is great. It also means sometimes we have to fix mistakes other teachers made.
This fact came to mind last week as my classes worked on proportions. Some students referred to something called the "Fish Method." Let's use this proportion:
Start with the number in a fraction with x (in this case, 8). Draw a line from the 8 diagonally up to the 2 (multiply those numbers), curve down to the 3 (divide by that), then diagonally up to the x (your answer equals x). What you've drawn looks kind of like a fish.
To be clear, this isn't a "mistake" I had to fix. Rather, it's a case of students clinging to a method that only works in a limited number of cases. For instance, proportions like these had them flailing.
We had to discuss other methods that had broader scope. This isn't a bad thing—I'm all for discussing multiple methods and their respective limitations. But whenever something like this comes up, I try to tread lightly. I don't want to say that their other teacher was wrong, bad, or not as cool as I am.
There are other situations, though (not like this proportions situation), where that's exactly what I'm thinking. It even happened to me as a student. When I was very young, I was told by a teacher (a student teacher, to be fair) that "it's" always has an apostrophe, whether the contraction or the possessive. Yes, really. It took me a few years to (a) figure out she'd been wrong, and (b) correct my bad habit.
I'm sure it can go the other way, too. A teacher instills all kinds of wonderful things in a student, and another teacher down the line destroys all that work.
Is there a way to avoid it? Maybe not. There will always be human error, whether intentional or not. All I can do is try not to be one of those "bad" teachers, and try to repair damage where I find it.
Have you observed or been affected by cases of teachers working against each other? How did it impact you?