Some students are more communicative than grammar-minded. Some learners have studied grammar for years, but they have practically no experience of oral communication. Some adult students are 'rusty'. Target marks sometimes have to be adjusted, and I make an effort of being aware of this all the time. One advantage with target-oriented education is that there are no 'surprise' marks at the end of the course.
Many countries have national normative tests in English.
In distance education programmes it is a necessary practice to set not only individual targets for marks but also to specify the dates for individual final exams already in the early planning stages of the course. Without diagnostic entry tests that is much more difficult.