When will they learn?

Maybe network executives will think about scheduling their serialized dramas more logically in the future — not because it's good for us, but because it's good for them.

Recently, popular serials have proven to be considerably less popular when they return after long layoffs.

"Heroes" returned last week after a seven-week layoff and the ratings are not what they were. According to Nielsen Media Research, just under 12 million people tuned in to the April 23 episode; the series had averaged 14.7 million viewers before the long break.

Part of that was certainly due to the fact that "Heroes" had to compete with ABC's hit "Dancing with the Stars." But, just anecdotally, I know a number of people who were surprised to learn that a new episode was on.

That's the danger the networks run when they interrupt series for weeks on end. TV viewing becomes a habit. And it's not that hard to get out of the habit.

CBS split "Jericho's" season in half — 10 episodes last September-November; a three-month hiatus; 12 more episodes February-May. And 2 million viewers walked away during the hiatus.

Again, the competition increased — "American Idol" returned — but these are not isolated examples. For all four years that "Everwood" was on the air, the first episodes back from a hiatus always showed a big erosion in viewership.

And it's not a phenomenon limited to new shows. It happened to "ER," and that show is in its 13th season.

The former ratings champ had fallen off in recent years — so much so that NBC announced it would disappear for 13 weeks in the middle of the season to make way for "The Black Donnellys."

To everyone's surprise, when CBS moved "Without a Trace" to Sundays, "ER" — despite a weak lead-in from NBC's Thursday lineup — resurged and reclaimed the top spot in its time slot. From September through April, every original episode of "ER" beat CBS's "Shark" in all the demographics that counted and, more often than not, in total viewers and households as well.

Then "ER" took a seven-week break from February-April. Its first week back, "Shark" beat it for the first time in the 18-49 demo and every other measurement that counted. In its second week back, "Shark" beat "ER" again. And so did ABC's "October Road."

The fact is that these series can't run 30 or 40 weeks a year. Even if the writers could turn out more than 22 or 23 episodes a year, it would be prohibitively expensive to produce.

And, frankly, I'd rather see 22 good episodes than 30 that aren't so good.

But the scheduling is often unforgivable. Start running these shows when you can air all your episodes as close to uninterrupted as possible.

Frankly, I'd rather put up with 20 weeks of some dumb reality show if I could get 22 weeks of "Heroes" without the two seven-week breaks we had this season.

There's evidence to indicate it would help the ratings. Good for us, good for the networks.

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E-mail: pierce@desnews.com