The students at Harrison Middle School are being split into groups for a community service project. The school faculty has decided that each grade (6th, 7th, and 8th) will be split up into their own set of groups. The faculty has also decided that it is important for each grade to be split evenly into groups, with no leftover students, so that each group in a grade has exactly the same number of boys and girls. For each of the following grades, determine the largest number of groups that can be made and the number of boys and girls that will be in each group.
The 6th grade has 64 girls and 72 boys.
The 7th grade has 81 girls and 63 boys.
The 8th grade has 68 girls and 60 boys.
Which grade group has the largest number of students in each group.