I might respond by first agreeing the poor grades must be addressed and a plan to get the children back on track is necessary. I might also express your desire to get to the root issue as to why the grades have dropped so drastically.
You said the children always had good grades before the divorce. While the workload may have increased as they move from grade to grade certainly there is more than just an increased workload or a more difficult curriculum causing such poor grades.
I would agree/validate your W's idea of a concrete plan on how to bring the grades up (tutoring, school work at home, having a parent check the list each night) but also be very clear in YOUR desire to find and address the root cause of the poor grades.
