if the captions with the images are correct, then they show us a group of grade nine students still with the same teacher they had during the previous two years. That would make 9th grade of the Class of 1960 still at one of the feeder schools, not at Mercer Island High School.
Sophomore = 10th Grade
This is the first group image in which one of the girls has been definitely identified by her own daughter. The same girl also appears in the 'french club' image, though no year is given...and she is there in the ninth grade, easily recognized because she's wearing the same clothes as one year later. We gather her parents must have been frugal.
Junior = 11th Grade
Senior = 12th Grade
We have no group images of the 11th or 12th grade. The only image that bears a date caption of 1960 is oddly enough, the 'no sweater image' which belongs to the daughter of the girl who has been identified...and she has evidently cropped and tinted the image and texturized it, because the original french club image appears to have been black and white...
The girl wearing the glasses holding the book in the french club image is the same as the girl standing next to the image of Stanley Ann Dunham in the 'no sweater' image. Get the picture? BTW, I know it doesn't look all that much like her, but the daughter should know her own mother, who is very much still alive.
PS. That's Maxine on the far left, back row, top image