text: Have them do more in class. Have them write a journal entries that stay in the classroom. This way you have a caliber of work that the are producing at rough draft level. Have bigger assignments with in class work, ask to see rough drafts and the work in progress. Praise the students that you know are making an honest effort and praise each improvement. Basically use the same techniques that teachers use for native language students. You do them little good if they are having others do the work or buying the work, they still have not mastered the skill they need. You may want to mention this to the class as being an important part of learning, that honesty and hard work matter, you may want to incorporate the writting into quizes and have a comprehensive exit exam as well so they know there is a reason to do the work themselves. Note cards outline rough drafts, and most people will not cheat, it is too much effort.