"the Sample files use the Payroll Center, which is no longer available in the versions used with the textbook"
That Payroll Center is Active because the Payroll Function has a Sample Code that makes it show in that File.
"Since the Payroll Center is gone from the 2018 version"
It's not the Program that controls this. It's your File. Any time a file has Payroll functionality, whether for real or for Sample Purposes, the Payroll Center is also revealed. It isn't enabled under Manual Payroll. Manual Payroll gives you about 2/3 of the functions.
This makes no sense, and seem a bit conspiracy theory: "that QB is engineering this to get them to purchase QB's own payroll services"
Because they still allow users to use Manual Payroll, and they still partner with the School Material providers to enable them to use Files with "pretend" payroll.
I would contact whoever is providing your school materials. You didn't say what is the source of the training material you are using in this classroom.
"and I taught using it for years in the 2015 version, so I know how helpful it was"
I started teaching QB in the classroom with QB 2007. I also teach Manual Payroll to the students in my "QB and Payroll Class" as their optional setting, but we work through the actual Payroll Center and functions, because the Student File has all of this in it. I have evaluated lots of student material, used material from Intuit, Sleeter, Michelle Long, and Logical Operations, as well as contribute to the material in use by two different publishers.
