Toaroha Schist is not specifically assigned a grade as it is a type of rock formed from the metamorphism of sedimentary layers. The term schist refers to a medium-grade metamorphic rock that is characterized by its foliated texture. The grade of metamorphism can vary within schist, ranging from low-grade to high-grade. Therefore, it is more appropriate to refer to Toaroha Schist as a type of schist rather than assigning it a specific grade.