Putting together a primetime lineup takes more than just throwing darts at an empty schedule. (Well, most of the time.) As the networks put together their fall plans, it's up to the scheduling executives to parse test-audience scores, research data, producer pleas and gut instincts to determine which new and returning series should make it and when they should air.

But sometimes serendipity steps in, and a show will either land on the schedule or fall out of favor for unusual reasons. "Weird things happen every year," says one insider. "You think you're done, and then some crazy thing comes along." Before they sat down this week to start screening this year's batch of comedy and drama pilots, we asked a group of network-scheduling execs to share some unusual ways their programs made the grade or fell short.

First impressions CSI was an afterthought at CBS in 2000, as all of the attention was lavished on a reboot of The Fugitive. There was even talk that the pilot might not be screened by execs, partly because of the dark subject matter. "There was concern about it being too gory, and it was almost written off," says one exec. But strong test results got the show on the air. How unsure were execs? Even after CBS picked it up, Disney, which originally developed the show under its Touchstone TV banner, dropped out— believing there was no chance that CSI would be worth the investment. Oops.

Another show that might not have made it to air is NBC's ER in 1994. As former entertainment president Warren Littlefield recounts in his new book, Top of the Rock. Littlefield says his boss, then-NBC West Coast president Don Ohlmeyer, wasn't a fan, and the show was potentially DOA — until testing results came back, and the positive reaction was through the roof. Says another exec who was there: "Ohlmeyer hated ER. He didn't like it and Homicide was going there. [ER] was dead. Then it became the highest testing of all time."  In 1996, The Pretender wasn't even initially screened at the network, but the show wound up being the highest-testing pilot since ER and that was enough to make the grade. "I believe in testing," says one exec. "It matters more than people want to admit. I do think it's a mistake not to listen to what viewers are telling you."

The power of youth When ABC screened the quirky Ugly Betty in 2006, execs didn't like it. But ABC's young assistants were such ardent fans that the top brass couldn't ignore it, and reconsidered their stance.

The coin flip In 2000, Fox originally scheduled new dramas Freakylinks and Night Visions on Fridays, but later (after the network's primetime ad sales were completed, naturally), the network decided to put the reality show World's Wildest Police Videos at 8pm instead. That meant the network had to pick one of the dramas to air at 9pm and push the other to later in the season. "We talked about which one to pull off, but decided that it didn't matter." Fox's scheduling head flipped a coin, which landed in Freakylinks' favor. Night Visions showed up the following summer, but neither show lasted long.

Mad TV NBC's Mad About You almost didn't make it off the ground after test audiences objected to a scene in which Paul Reiser and Helen Hunt have sex on a kitchen counter. But viewers found the couple so likable that the show survived. "It was a strong, high-appeal couple in an off-putting story," says one exec. Not as lucky: A 2004 CBS pilot starring Kirstie Alley as the mother of Ricki Lake. The pilot was considered a shoo-in for air until the testing data came back. "It was on the schedule," remembers one exec. "The magnetic strip had a place on the scheduling board, it had a timeslot, which is not all that unusual, a lot of shows that look promising do. This one looked more promising than most. But then the research came in." Test audiences loved the relationship between Alley and Lake but were turned off by a risqué storyline involving Lake's character's 10-year-old son.

Stern warning Daniel Stern's 1999 CBS comedy Partners was a contender until Stern allegedly left a voicemail for CBS boss Les Moonves, trashing the show and telling him he refused to star in it. CBS didn't pick up Partners, and producer Columbia Tri-Star TV sued Stern, claiming he sabotaged their pickup. Stern countersued; they settled out of court.

What works Sci-fi shows with a certain point of view do surprisingly well when tested with audiences, so much so that networks monitor false positives. Also, "warmth, and shows where you feel a connection with some characters" tend to get a positive reaction. And "the less confusing a show is, the better off you are," an exec says. "Connectivity and clarity are the two things that drive success in a pilot."

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