It’s been a rough spring for NBC, which is mired in fourth place for the third straight year among adults 18-49 and down 6 percent from last year.

But there has been one bright spot for the network, and that’s its improved performance this year among teenage viewers. It’s the only major demographic where NBC has shown growth.

Of course, NBC still ranks fourth among the Big Four networks in the demo, but the jump comes in a year when the Big Four’s collective average among teens is down 4 percent year to year.

Season to date, NBC is averaging a 1.4 in teens 12-17, up 8 percent over last year’s 1.3, according to Nielsen data analyzed by Fox. First-place Fox is averaging a 2.6, down 7 percent from last year’s 2.8. Second-place ABC is down the most, 15 percent, from a 2.0 to a 1.7, while CBS is up 7 percent from a 1.5 to a 1.6.

The bulk of NBC’s growth can be attributed to “Heroes,” the first-year drama that airs Monday at 9 p.m. While “Heroes” has fallen in several demographics since it returned from two months of repeats a few weeks ago, it seems to be strengthening among teens.

Last Monday’s episode averaged a 4.5 in 12-17s, up 15 percent from its 3.9 average last fall.

By comparison, “Heroes” averaged a 5.4 in 18-49s last week, down 17 percent from last fall’s 6.5 average.

“Heroes” was the No. 5 show on broadcast last week with teens, behind Fox’s two editions of “American Idol,” “House” and “Family Guy.” It even outdrew ABC’s two-hour “Grey’s Anatomy” special.

Also doing quite well among teens for NBC is “The Office,” which may be a surprise considering the sophistication of its comedy and the fact that the show lampoons an office culture teens are too young to have experienced.

An expanded episode of the show last week that lasted nearly an hour averaged a 1.9 in 12-17s, making it broadcast’s No. 2 non-animated comedy behind CBS’s “Two and a Half Men.”

And it’s possible that NBC’s teen ratings will continue to rise next year. In addition to the fall return of “Sunday Night Football,” one of the year’s top shows with 12-17s, NBC is rumored to be picking up a remake of “The Bionic Woman,” whose sci fi theme is reminiscent of “Heroes” and could fit nicely with it on Monday nights.

Meanwhile, in other younger viewer ratings for the week ending May 6:

Among teens 12-17: Fox was first with a 2.8 rating and 10 share, followed by ABC at 1.7/6, the CW at 1.6/6, NBC at 1.3/5, Univision at 1.2/4, CBS at 1.1/4, Telemundo at 0.3/1, Telefutura at 0.2/0, and Azteca at 0.0/0.

Among kids 2-11: Fox led with a 2.0/8, followed by Univision and ABC at 1.2/5, CBS at 0.9/4, the CW at 0.9/3, NBC at 0.6/3, Telemundo and Telefutura at 0.3/1, and Azteca at 0.0/0.

The top five shows among kids 2-5: 1. “Mickey Mouse Clubhouse” (Disney, Saturday 9:30 a.m.); 2. “Go Diego Go” (Nickelodeon, Wednesday 9 a.m.); 3. “Mickey Mouse Clubhouse” (Disney, Saturday 9 a.m.);4. “Dora the Explorer” (Nickelodeon, Wednesday 9:30 a.m.); 5. “Blue’s Clues” (Nickelodeon, Tuesday 10 a.m.)

The top five shows among kids 6-11: 1. “American Idol” (Fox, Wednesday 9 p.m.); 2. “Hannah Montana” (Disney, Friday 8 p.m.); 3. “American Idol” (Fox, Tuesday 8 p.m.); 4. “Cory in the House” (Disney, Friday 8:30 p.m.); 5. “The Suite Life of Zack & Cody” (Disney, Friday 10 p.m.)

The top five shows among kids 9-14: 1. “American Idol” (Fox, Wednesday 9 p.m.); 2. “American Idol” (Fox, Tuesday 8 p.m.); 3. “Hannah Montana” (Disney, Friday 8 p.m.); 4. “Ned Declassified” (Nickelodeon, Tuesday 6 p.m.); 5. “The Suite Life of Zack & Cody” (Disney, Saturday 7:30 p.m.)