I feel for you. DSD1 and 2 are both not particularly academic. They are, however, both funny, kind and caring and I'm proud to be their SM. They're so much more than their clutch of Ds, Es and DSD2's two Cs.
They were both in different schools for GCSE (we'd moved catchment areas and DSD2 went to the better school as it happened- not academically, but pastorally). It is very obvious- not in their results, but in their confidence. DSD1 was on fluoxetine and still goes to CBT for her anxiety. She never 'achieved' anything because her targets were always aiming for the impossible. She wasn't congratulated on getting a D, she was told she needed a C, and she, and the school, knew that wouldn't happen. Thanks to that, she completely lost interest in school. Why put effort in when it wouldn't make any difference?
DSD2 was told she was so much more than her GCSEs. On the careers evenings, she was guided and supported. She wasn't told she'd only end up working at KFC, she was told that there were so many worthwhile, useful and rewarding jobs out there she could do, even if she didn't see it (or the jobs) that way. She wants to be a plumber, as it happens, and is excelling at college.
I get teachers have a lot of pressure, but even just adding on a 'but don't worry, if you don't achieve a C, there are so many options out there, it isn't the be all and end all' when talking about their expected results would help.