Teachers, whose first official work day was Monday, Aug. 13, appeared to take it in stride, while not exactly rejoicing at the early start.
"I don't love it, but I understand why they're doing it," said Susie Deutsch, a fourth- and fifth-grade teacher, as she worked to assemble her classroom Monday afternoon.
The hotly debated early start date is the result of a shift in the academic calendar to squeeze in the first semester before the December holidays. It also means the school year will end earlier than usual — May 30 instead of mid-June.
"It does make sense to me, but it's been a short summer," Deutsch said, adding that teachers were extensively polled about their views on the calendar before the change was made.
Juana Briones librarian Julie Griffin said "the jury's still out" for her on the new calendar.
"Obviously it cuts vacation time and all that good stuff, but in the end, when we're finishing the year in late May it might be really nice.
"It will be interesting to see how ready the students are."
Ready or not, Palo Alto students flocked back to classrooms on Thursday.
At some schools, the early start date was overshadowed by massive construction projects right in the middle of campus.
Jackhammers and backhoes thrummed earlier this week at Jane Lathrop Stanford Middle School in a space between classrooms and the school's gym that's typically a major gathering spot for students.
JLS students can look forward to the end of construction in early 2014, when they will occupy new science labs and 10 classrooms in a new, two-story building.
As officials work to modernize campuses and keep up with enrollment growth, major construction also is underway at Gunn and Palo Alto high schools, Jordan and Terman middle schools and Fairmeadow Elementary School, with a groundbreaking for major construction at Duveneck Elementary School likely in January 2013.
The district-wide construction, which will touch all 17 campuses, is being funded by a $378 million school-facilities bond, which was approved by more than 77 percent of voters in 2008.
With the recent enrollment bump showing no signs of slowing, school Superintendent Kevin Skelly will ask the Board of Education next week for "authorization to start preliminary work on exploration of a fourth middle-school site," possibly at the old Cubberley High School property.
As for this fall, "with the exception of kindergarten and fifth grade, we are very tight at every grade level," Skelly told school board members in a preliminary report on enrollment Aug. 10. Some classrooms will exceed by one student the standard class sizes of 22 in first grade, 23 in second and third grade and 24 in fourth grade, he said.
Kindergarten enrollment is expected to be down over the next three years as a new state law is phased in requiring that children be 5 by Sept. 1 of the year they begin kindergarten. Previously, children could enter kindergarten if their birthday came by Dec. 2.
The district will take an official 2012-13 headcount after Labor Day.
"It seems that whether we're in a boom time or recession, families continue to move to Palo Alto so their children can receive our quality of education," Skelly said in remarks to teachers as they convened Monday morning before scattering to their classrooms.
Though Palo Alto's first day of school was its earliest ever, it was not the earliest in the area.
Back-to-school dates for public schools in neighboring districts ranged from Monday, Aug. 13, at Los Altos and Mountain View high schools to Tuesday, Sept. 4, in Menlo Park elementary schools.
Los Altos and East Palo Alto elementary students, as well as Menlo-Atherton and Woodside high school students begin school next week on Thursday, Aug. 23.
Nearby private schools' start dates vary: Aug. 23 at Menlo School, Aug. 27 at Pinewood School and Gideon Hausner Jewish Day School, Aug. 30 at Castilleja School and Sept. 4 at Mid-Peninsula High School.