I don’t think you can evaluate just the use of evidence. Their evidence must support an argument of their creation. If their argument isn’t sound, or their words are too jumbled to make sense of what they’re trying to say, then there’s no way to effectively evaluate their use of evidence.

Just last week I said to a student: “You’re not using this source to its full potential. In fact, what you use here isn’t supporting your argument at all if what you’re saying is ‘x’. You would be better to use *this* chunk from this source rather than that one.” While that sort of implies that one can evaluate evidence independently, what I discovered through this conversation was that the student didn’t mean what was worded and that’s why her argument and evaluation/discussion of the evidence refuted/or didn’t support her thesis.

So that doesn’t make much sense as I look at it now, but it sure did at the time. However, I stand by my claim that teachers cannot evaluate evidence independently of the rest of the argument, thesis, use of rhetorical devices, syntax, punctuation, usage, and all the other “stuff” we get caught up in when assessing student writing.