I noticed that there are a few inconsistencies in what I was taught throughout my English education, and I hope to clarify them. I think the nature of the question is somewhere between "grammar" and "English pedagogy."
*I apologize ahead of time if this question is not appropriate on Writing stackexchange. I am new to the community. Please feel free to migrate the question to other communities, as appropriate.
**For context, I am a student in the natural sciences who had most of my education in the U.S., but am from a non-English speaking country.
Here are a few examples of such contradictions:
I.) In high school, I was taught not to write "run-on sentences," but in college, I was not discouraged from doing so. In fact, many authors I read seemed to write run-on sentences in a lot of places.
II.) In high school, I was told not to use passive voice in my writing. (The reason I was given was that it unnecessarily makes sentences longer.) Again, I was not discouraged from doing this in college.
A more extreme example:
III.) In elementary school, I was taught that an essay should consist of five paragraphs. (There were additional specifications on what these five paragraphs should look like.) This was obviously not what I was taught in high school and college.
I assume there are these "inconsistencies" because writing is a very hard thing to teach, and that it makes at the very beginning to teach them with a lot of rules and constraints (as in Example III). Then as the student matures, teachers teach students a more refined version of what is considered "good writing." Therefore, many of the rules from earlier are taken away.
Is there a general consensus (amongst, say English educators or academics) on how English should be taught? (In particular, if it is fine to use passive voice in one's writing or to have run on sentences?)