One problem with teaching technical writing is that very little of the actual job of technical writing is about writing.
What the job is about, instead, is project management, needs analysis, interviewing, going to meetings, collaborating with brilliant intractable people, and learning complex technical subjects quickly.
Technical manuals are not so much written as they are assembled.
The raw materials for a manual--code, specifications, engineering release notes, customer data, marketing materials and white papers--all exist in some form within the organization.
The overall structure of the manual is usually pre-determined by the style guides and prior publications of the organization.
Given all this, and given that the main thing a beginning technical writer needs is a portfolio, I think that I would teach a technical writing class by sending the students out to complete real-world assignments.
I'd send students to the local hospice organization to write a two page user-guide for the person who enters client data into an excel spreadsheet. Or I'd send them to the local schools and have them write instructions telling teachers how to use their computers.
Then I'd have them conduct a usability test of their procedures, and revise accordingly.
By the end of the course I'd want them to have a portfolio piece: a tested, readable and useful user-guide.