This the information I provided for prospective participants while I was collecting data:
"I'm interested in finding out how the CEFR descriptors work when you use them to assess learners. I ask you to do this in two ways: first to assess two learners whom you know well, so you are able to judge several aspects of their competence; then to assess some samples of writing by learners whom you've never met, so you can only judge some aspects of their writing (but you have an actual example of this in front of you)."
In practice, this is what I asked participants to do:
All of the information that you sent was treated as confidential. I will not reveal your name, or any information which might enable other s to identify you, in any publication. Similarly, I will not reveal the identities of any of your students. The samples of students' written work that sent and/or assessed are anonymous: all personal and place names have been removed.