You see, the online environment in which I teach has a way of setting up grading forms, and a way of assigning a grading method to an assignment, but it wasn't giving me the option of choosing "grading forms" as my grading method for the assignments I wanted to grade. There isn't nearly enough redundancy in WebCT, so I figured I was overlooking the right menu for the button. I downloaded the manual, all eight parts, and searched. But no... grading forms weren't even mentioned in the manual.
A web search eventually yielded minorly helpful documents, enough to keep me going a little further. Eventually, baffled, I tried making a new assignment - and behold, there was "grading forms" as a grading option. I resigned myself to doing without the forms for existing assignments and replacing all the not-yet-done ones with new, correctly done replacements. I decommissioned the old versions of the assignments by unchecking all the boxes which would make them interact with the rest of the site. At one point, I accidentally went back into an old version instead of its replacement - and there was the grading forms option. I didn't have to replace them all after all!
And that's how I found out that if I want to switch the grading method of an existing assignment to use grading forms, I must first mark the assignment as "Not gradeable", save and exit, reopen the assignment, and choose my grading option of choice.
My next complaint is that it won't let me put in negative numbers in the grading sheet.... but I don't think there's a workaround for that one. I'll have to manually track deductions instead.