As an educator who has had several twin pairs in my college classroom, I have seen both the benefits and the drawbacks of twins enrolling in classes together.
In a writing course I taught, a set of twin boys always sat next to one another, with one whispering constantly to the other. When I collected homework, only one twin, the verbal one, would hand in both twins' work, in identical handwriting. When I called on the less outgoing twin, the other twin would answer for him. I soon suspected that one twin was actually doing both twins' homework, and found my suspicions to be correct. The more verbal twin confessed to me that he had been the "communicator" for the two of them since they were very young. They had always been placed in the same classrooms in school, and his more silent brother had very few academic skills and was quite passive-aggressive with him--so he felt pressured to perform for both of them.
In a literature class I taught, twin girls enrolled together. One would turn in "A" work, the other "D" or "F" work. When I spoke to the "D" student to inform her she was failing the course, she began plagiarizing her sister's homework, stealing it from their common computer when her sister wasn't home. When I confronted both sisters separately, they both told me that the sister turning in "D" work had suffered complications at birth. Their parents had always identified the "A" twin as the "good twin", and the "D" twin as learning disabled. The twins had been separated in school because the "A" twin was always placed in accelerated courses, and the "D" twin was in lower-level courses and sometimes special education courses, even though she had never been assessed for a learning disability, to her knowledge. By signing up for my college class together, they had hoped that the "D" twin would learn better study habits from her sister--but instead, she committed a desperate act, because her family had taught her that she couldn't learn.
Now I find myself in an interesting situation. In 2005, I gave birth to twin boys. As a teacher, I have seen firsthand how decisions about whether or not my sons enroll in classes together can affect their lives. Most importantly, by getting to know twins in my classes, I've decided that I will reconsider each year whether or not my boys should be in the same class. Parents of twins need to be aware of unhealthy dependence that can occur when one twin cannot or will not perform academically, and the other twin feels pressure to "cover" for the other. Parents also need to resist the temptation to label or compare academic or mental abilities of twins, for instance singling one out as the "artistic" one and the other as the "math whiz". Avoiding these pitfalls is not easy; often, twins are not fully aware of the roles they have taken or the roles that have been assigned to them, consciously or not, by their families. However, in order to ensure the happiness and success of both twins, it's important that parents remain objective, aware of the academic dynamics between the twins, and willing to reconsider from year to year their decisions about whether or not to place their children together in a classroom.