I just posted this question, however I felt that it needed another tag describing the interaction between courses, and also a group with academic problems, but after reading the list of existing tags I couldn't find any that fit. May be I skip them, may be those situations don't need tags, I want to know first before trying to make them appear.
In response to the question and comments, here are some ideas:
One possibility is course-connections, and I would suggest that the description indicate clearly how this tag differs from prerequisites. We could potentially only use the former, and allow it to subsume the latter; however, I think the type of questions being posted to ask about connecting material from different courses vs. asking about prerequisites for a course will be sufficiently different so as to justify making a new tag.
(Incidentally, my sense is that the linked question might be closer to prerequisites, but that is perhaps best left for the OP to decide.)
Another possibility is to note that the connections being made are really about connecting material. A casual way to indicate this would be with a tag named, e.g., making-connections, with the appropriate tag description. For example, the linked question is, to some extent, about students realizing "that sequences could be seen as functions." A drawback to this tag is its generality: A gentle counter-argument to my own suggestion would be, how often is learning/teaching mathematics not about making connections?
A third possibility is to introduce a tag such as teacher-interactions since, in my estimation, the key part of the accepted answer involves talking to the other teachers.
An irresistible side-note: One of the difficulties in wording this tag is that "class" takes on more than one meaning in the context of education, e.g., lower class (typically referred to now as lower socioeconomic status or low SES) as opposed to a class on algebra. The simplest workaround is to use the word "course" instead. This latter approach has at least two drawbacks. First, one of the terms around using/applying knowledge from one area in another area is "transfer"; but "course-transfer" is quite confusing, since it sounds more like credits are being transferred programmatically. Second, the typical prefix to denote between/among is "inter-", e.g., between/among disciplines would be "interdisciplinary" -- this road leads to a very particular issue with the word "course"...