Broadway B.O. took its typical swan dive in the week following the Labor Day holiday.

Almost every show on the boards took a hit, thanks to the back-to-school distractions of early fall. The only one that posted an uptick was “Million Dollar Quartet” ($495,360), which last week featured the added attraction of a one-night-only appearance by Jerry Lee Lewis, one of the four rock ‘n’ roll greats depicted in the musical.

Otherwise, the Street saw biz decline significantly in a week that paired the double whammy of Labor Day and the Jewish new year. Overall sales slid $3.3 million to $13.4 million for 22 shows on the boards.

Box office had seen a notable drop in August, a premature falloff that was possibly due to the early start of the school year skedded at many campuses around the country.

Last year saw sales decline gradually throughout the end of the summer, rather than drop suddenly, as has often happened in the past. Total sales during the same frame in 2009 fell just $400,000 to $15.4 million for 22 shows.

Twelve months ago, though, more previewing shows had joined the lineup by this time, as opposed to the two new offerings — “Mrs. Warren’s Profession” ($179,981 for seven previews) and “Brief Encounter” ($123,695 for five) — on the boards. Besides, last year benefited from the record-setting grosses of Hugh Jackman-Daniel Craig topliner “A Steady Rain.”

Overall attendance last week sank to about 71%.

Among the individual productions on which a hefty toll was taken, “The Addams Family” ($806,698) fell by 25%, which raises some doubts about the production’s durability against seasonal Broadway trends. Another habitual member of the millionaires’ club, “Promises, Promises” ($825,154), also fell down the ladder of the top 10.

Largest overall falloff was seen at family-magnet “Mary Poppins” ($558,088), which slid 34% in a week during which “In the Heights” ($407,974) and “Fela!” ($344,626) each fell by about 30%.

Dip at “American Idiot” ($430,449), also down around 30%, was exacerbated by the fact that the show played only seven perfs last week, missing one so that cast members could perform on “America’s Got Talent.”

If prior years are any indication, Broadway can expect to regain steam gradually over the fall as rookie productions join the lineup and auds can start thinking about going back to the theater now they’ve gone back to school.