Tucked at the bottom of a TV Guide Canada cover from February 2002 is a picture of four kids sitting on the steps of a school.

Above that picture is a headline branding Degrassi: The Next Generation, then only four months old, one of the best five TV shows people weren’t watching.

More than 10 years later, and 33 years since the TV story was first conceived, Degrassi is still on the air. The franchise, which also includes The Kids of Degrassi Street, Degrassi Junior High and Degrassi High, is now the longest running Canadian drama ever, with more than 400 episodes.

On Friday, it caps off its fall season when the Degrassi kids head to Las Vegas for the show’s third TV movie in four years.

The show has changed dramatically since it appeared on that TV Guide cover. Now in Season 12, the faces are different, as the original Degrassi: The Next Generation cast have all “graduated.” Even the name of the show changed when Degrassi dropped the Next Generation part of its title in 2010.

What hasn’t changed, its executive producers say, is the school and the problems the kids inside inevitably will have. And that’s the secret to Degrassi’s durability.

Sitting in her office in the middle of the Degrassi universe — in reality, that’s the Epitome Pictures backlot studio in East York, where almost all of the show is filmed — executive producer and co-creator Linda Schuyler explains that it took a couple of failed experiments to figure out that Degrassi is about the school, not the characters.

After five seasons of The Next Generation, it was time for the classmates who started that series to graduate, and those characters had become very popular.

“We were really nervous about it. And the broadcasters were nervous with us. We said, ‘Those characters have got such audience loyalty that we have to find a way to keep them in our show.’ So we actually did. We built a university house,” Schuyler said.

They did the same thing two seasons later when the next group of Degrassi students graduated, this time building a university dorm setting.

“What was really fascinating to us is when the audience research came back over these two experiments, the audience loyalty was actually not with characters, but the audience loyalty was with Degrassi. It was with the high school experience,” Schuyler said.

“That was a real eye-opener for us and, at the same time, very liberating.”

After that, Degrassi started introducing a crop of new, younger characters every season or two as they bid farewell to beloved graduating characters. The show has told stories about more than 50 different high school students.

“Sure enough, everybody says, no, we’ve got to carry on (with the old characters). But then they fall in love with the new ones. Hopefully,” said Stephen Stohn, Schuyler’s husband and a Degrassi executive producer.

Degrassi conducted another experiment in 2010 — the franchise’s 30th anniversary — by doubling its episode count to 44 a season and switching to teen-oriented MuchMusic from CTV. This experiment was a resounding success.

Unlike CTV, MuchMusic can show Degrassi four nights a week in the summer and often runs fun promotions with the young cast, like live chats and screenings in the parking lot. The show premiered with 1.4 million viewers and became MuchMusic’s most popular show ever for viewers aged 12 to 34.

Around the time the series switched to Much, Degrassi created Twitter accounts for each student, to let fans interact with characters as if they’re classmates.

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It’s similar to the universe Degrassi created when the Next Generation show began. Its now-defunct Degrassi.tv website let fans enrol in a “virtual” school where they could participate in student council elections and interact with characters by writing on their “lockers,” an advanced form of social networking in 2001.

Keeping fans engaged with the school, Stohn said, seems to correlate with increased viewership, whether that’s on TV or, increasingly, on other platforms.

When the show airs, Stohn will often watch it with Twitter open so he can read fans’ reactions.

“I can tell you pretty closely what the Nielsen overnight ratings are going to be the next day from the reaction on Twitter as the show is happening. Are we trending? Where are we trending? What’s the reaction to characters?

“It’s not an exact science, but I almost prefer the Twitter reaction. I think it gives me a better sense of how the show’s doing than the Nielsens do sometimes.”

As Friday’s Degrassi: Viva Las Vegas special airs, with several episodes in Season 12 still yet to come, the planning continues for Season 13.

This will be the 33rd year Degrassi has been in Schuyler’s life. The executive producer is 64 and a lot of her friends are retiring, but she has no plans to ditch teen drama for a slower paced life.

At Degrassi’s American broadcaster, where the show has been ranked No. 1 every year since it premiered there in 2002, people used to chant “Degrassi forever!” when Schuyler and Stohn visited TeenNick network offices.

Degrassi may not last forever, but Schuyler plans to keep the franchise going as long as it’s still relevant — as long as teenagers can see a bit of their own high school within the walls of Degrassi Community School.

“I’m as excited now about Degrassi 33 years later as when we first launched it.”