Maybe I'm missing something here, but why would you want to hide anything from your student? You should be as frank with them as necessary, the only exception I can think of being where this is going to demoralise them and affect their progress in which case you should counter every negative with a positive.
(One other exception, and that is trial lessons who clearly have no intent of coming back, but ask how well they did because they want to impress family and friends. These students are always excellent!)
Come to think of it, why are you students even asking you about their progression? I discuss my students' progress with them as part of the debrief on every flight, to a greater or lesser extent.
FFF
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