When the series is set in a high school environment, an added condition exists – the four year time frame in which students attend the school. Further, because of the need to establish the show’s back-story of each character's place in their high school social sphere, most main characters are often around age 16, possibly sophomores or juniors, when the series debuts. This writing choice cuts this four year time frame down to three or even two years, and is the exact situation the Glee writers currently face in planning season three and beyond.
Within the context of most state’s laws that that children have to turn five by some date within the fall of the school year in order to begin kindergarten, students can be sixteen as early as the fall of their sophomore year until as late as the fall of their senior year – which is generally the case. Thus, there is some room for creative interpretation of character’s grades and ages initially. However, if writers want to establish a character as a junior in season two, for example, they may need to redirect attention toward that choice and downplay evidence that the character could have been interpreted as a junior in season one.
Glee characters Finn and Quinn, for example, could be interpreted as juniors in the show’s early episodes. They are sports captains, among the most popular kids in school - statuses often associated with upperclassmen. On the other hand, both characters also seem to be within the heart of high school experience, with the world outside of McKinley High still distant and ambiguous, so it’s possible that they are only sophomores. Further, having these characters their achievements so early on within their high school life could be viewed as a creative decision - have two characters ascend their high school social ladder with relative ease, only to have it collapse beneath them.
I don’t think the writers developed the initial storylines with a particular grade for Finn, Quinn, Rachel and the other students in mind – and that’s okay. As I described above, few television shows do so. While this summer has been filled with contrasting information about what grades the characters will be in during season three, I see some definite indicators of the characters’ class years.
Foremost, all of the students, with the exception of Sam, will be in the glee club this season. Therefore, if any of them could have possibly been juniors in season one, the writers have established that they were freshmen and sophomores then. Otherwise, they would have graduated at the end of one of the first two seasons. Why no upperclassmen were in the glee club in the first season is a gray area, but plausible given how unpopular the club was at its outset.
The other critical evidence lies in Finn’s comment to Rachel in last season’s finale, “Graduation’s a year away.” This comment, illustrated above, refers to Rachel’s ambivalence about reuniting with Finn given her interest in moving to New York after high school - an interest she is not sure Finn shares - and Finn’s reassurance that she has a year left in Lima before she has to make that decision. While it’s possible that Finn could have been describing Rachel’s graduation being a year away, rather than both of theirs, this seems unlikely. Their relationship is an archetypal one – the unpopular girl and the popular boy, and the idea of Rachel being older than Finn neither parallels that image nor has it been suggested on the show. Furthermore, if Finn was originally written as possibly a sophomore, possibly a junior in the first season, as explained above, it doesn't make sense that he would be a freshman in the first season. Therefore, it’s fair to conclude that Rachel and Finn will both be seniors this season, and most reports seem to support that.
In summary, despite some contrasting information about what is in store for Glee this season and beyond, the characters' grades have been established well enough for the writers to define them in the beginning of the season and proceed accordingly. As long as they do so, developing storylines with most characters’ impending graduations in mind, I'm optimistic that it will be a good year. After that? Maybe I’ll watch, maybe not. Either way, I don’t have any plans until then.
For those interested in further reading (especially for characters not addressed here), I recommend this article from showthemwhat.blogspot.com.