Grade 8 can be a year full of ups and downs, and this is to be expected. So as a mother refrain from being too reactive no matter what happens. As a former middle school principal I have dealt with many exasperated parents who can't understand their child's behaviors, study habits and his friends.
Just keep everything in perspective and consider the philosophy of 'this too shall pass'.
The most important thing you can do without being too 'motherly' is to help your child develop good study habits. High school is a whole other experience, and studying is often the #1 issue facing students when they transition to that level.
Study habits- what a wonderful thing parents can do to help their child succeed forever! Good luck!