The question came up on an online mail list: how can we get 1:1 students to stop using online translators to work on writing assignments?

I’d say the first step is to look at your writing assignments carefully.

Many times we are tempted to just say “write something”, and when we do that, the students’ minds naturally flow far beyond the language they know. Teachers are pretty good at realizing what language is known or not known, but students aren’t. They also rarely know the full scope of what could be said using the language they do already know. If they can say it in the TL, they won’t look it up.
Try giving assignments that limit by:
–Providing a very narrow topic or story line;
–Provide picture or other prompts to direct output;
–Prohibit the use of any language or vocabulary that is not already in the student’s head;
–Limiting time to write (as in timed writings) to force direct output of acquired language
And have students interact with their own writing:
–Read their own writing back out loud to you or another student — if there’s no fluency, it didn’t come out of that head
–Send students back to the texts — they can use texts that have been read in class as references while writing. Have them help their partner find a sentence that is like the one they want to say, and figure out what would need to be changed to make it work in the new piece of writing.
There needs to be a balance of frustration between “not being allowed” to write things they don’t know, and just being set free which results in a lot of random language often taken from other sources. But we need to look at writing assignments as opportunities to help develop writing, not just as output. There are writing skills we are trying to teach at the same time, or there should be. And for an L2 writer, you can’t get anything better than looking at a text written by a fluent writer and “borrowing” in an appropriate way (referencing the language and words used, not copying wholesale).