Patricia,
As a former science teacher, here would be an example of a categorization question I would ask my students. Categorize the following as either Biotic or Abiotic. Say they put one response as abiotic when it was biotic but got all the others right. Why would I want the student penalized for not classifying just one response correctly when they got the other nine options correct? It seems like a huge penalization for an 8th grader.
Yes, I COULD do this as a multiple-choice style, but getting the opportunity to do question types like this helps them practice for the types of questions they can see in our state assessments. Plus, as an instructor, it's less work for me to do one question worth 10 points.
This is why I would like to see partial grading on these question types.