Is there absolutely no way you can have any input? For example.. Start by grouping students and asking them to relate the findings of their investigation. Are there differences between what the students achieved? can they compare and discuss the differences in their investigation and make notes on these in case they want to consider them in the report? Could you stop the students a few times and show off examples of excellent work, either on screen or by holding up the book/page/whatever? Or is it literally an assessment in the sense that it's a work-in-silence-test? Can you postpone the assessment one lesson? Or does it HAVE to be there? If that's the case I would definitely call them and ask if they can change the date.