• by David Goetzl  @dgoetzl, March 1, 2007

Does Fox have another reality hit on its hands? Give it a few weeks.

Reality show "Are You Smarter Than a 5th Grader?" debuted with a boffo 10.8 "live" rating in the key 18-to-49 demo Wednesday, holding on to 95% of its "American Idol" lead-in. "Idol," which scored an 11.4 in the key demo in "live" numbers, ran from 8-9:30 p.m. and "5th Grader" followed for the next half-hour.

If somehow "5th Grader" could sustain its rating level--and that's dubious--it would rate higher in the demo than "Grey's Anatomy."

Fox said the premiere of "5th Grader" marked the higher-rated series premiere in the 18-to-49 demo on any network in five-and-a-half years, since NBC's "Inside Schwartz" in September 2001. On Fox, the debut was the No. 1 18-to-49 premiere in more than 13 years, since "The George Carlin Show," excluding a post-Super Bowl broadcast of "Family Guy."

But a debut with a massive "Idol" lead-in hardly guarantees an established hit, as a slew of shows have received gargantuan sampling, then faded.

"5th Grader" will have a chance to build a beachhead, however, with episodes following "Idol" last night, tonight and next Thursday--before testing the waters on its own starting on Thursday, March 15 at 8. There, it will face off against strong shows--CBS' "Survivor" and ABC's "Ugly Betty."

"5th Grader's" first two nights were half-hour episodes, and now it goes to a full hour.