I have decided to tackle this most difficult issue head-on. I start by calling the student's attention to his or her errors: I stop after the first phrase and ask what wrong notes were played. The student very often recalls them with remarkable precision, or at least spots the logical cause for whatever error was made.
We can then discuss the tension that led to the error, rather than just label it an error and hope that it will go away. Calling attention to it makes it possible to maximize the life of every tone, that is, the response to every tone, in other words, listening.