Ok, let's decode this... 1. "produces consistently accurate structures apart from "slips" characteristic of native speaker speech" This refers to the speakers use of grammar (structures). The speaker almost always (consistently)says (produces) sentences which are grammatically correct. When the speaker does make a mistake (slip), it's the kind of mistake that a native speaker might make. 2. "use a range of pronounciation with mixed control" This, of course, refers to pronunciation. I think they're considering all the different sounds of the language. The speaker can produce most of the sounds, but doesn't always get it right (mixed control). yes - "mixed control" means "unstable" or "inconsistent" in this case. Hope this helps!