(UPDATED, 10:37 a.m. Friday, with revised numbers from West Ada district.)

A scramble to add teachers and staffers in Vallivue, Twin Falls and beyond.

A portable classroom building at Madison Junior High School.

Emergency property tax collections. And perhaps, in Boise, an earlier-than-expected discussion about another building bond issue.

Across many of Idaho’s largest districts, preliminary enrollment numbers are heading upward, and that has short- and long-term implications. In the short term, class sizes will increase. In the long term, taxpayers may be asked to add new facilities.

The early estimates are just that: estimates. And they’re volatile. On opening day in Boise, Aug. 24, numbers were flat. Now, the district expects an enrollment increase of 450. Parents may have been thrown off by this year’s early start, deputy superintendent Coby Dennis said; it’s uncommon for Boise to start the school year two weeks before Labor Day.

The State Department of Education takes a few weeks to allow the numbers to shake out; statewide fall enrollment numbers won’t be released until Oct. 15. And the numbers will be revised again in February (the 2014-15 enrollment figures for this article are based on that Feb. 15 report).

To get a sneak peek at the trends, Idaho Education News checked in with the state’s largest districts. Here’s what we learned:

West Ada (2014-15 enrollment, 36,513). Enrollment is up about 950 from a year ago, Superintendent Linda Clark said Friday.

If this increase holds, it would represent a significant boost. In 2014-15, enrollment grew by about 400 students. And this year’s growth could prompt the district to collect an emergency property tax levy to help pay the bills. West Ada collected a $1.1 million emergency levy in 2014-15; unlike supplemental levies, emergency levies do not require voter approval. (Click here to see a list of the 13 districts that collected $6.4 million in emergency levies last school year.)

Growth in West Ada is commonplace; even during the Great Recession, enrollment increased by several hundred students each year. But this year’s boost appears in line with the area’s building boom of the 1990s and early- to mid-2000s, when it was not uncommon for the district to add more than 1,000 students each fall.

West Ada voters approved a $96 million building bond issue in March, and will put a two-year, $14 million-a-year supplemental levy on the Nov. 3 ballot.

Boise (2014-15 enrollment, 25,912). Enrollment is up by about 450 — a surprise to administrators who were expecting flat numbers.

The growth has occurred despite a dip in kindergarten numbers — which was expected, since birth rates dropped about five years ago, during the heart of the Great Recession. What was unexpected was a surge in newcomers. Some 1,500 new students have moved into the district, from other Idaho communities and from out of state. “They’re coming from all over the place,” Dennis said, “and it’s really strange.”

In the short term, Boise schools should be able to absorb the newcomers, and the district is planning to hire only eight or nine additional teachers. The longer-term issues are a bit more vexing. Boise has scrapped its open enrollment policy in crowded schools on the west side of town. And with new residential growth occurring in all corners of the city, trustees might have to start discussing another bond issue sooner than expected.

Boise last passed a school bond in 2006.

Nampa (2014-15 enrollment, 14,892). Enrollment may increase slightly, spokeswoman Allison Westfall said, and the district has “pockets of very full classes.” District officials are looking at their current staffing to see if they can make adjustments.

Bonneville (2014-15 enrollment, 11,887). Classes opened Monday, with 11,760 students on hand. “However, I’m sure we will have many more by mid-next week,” Superintendent Charles Shackett said.

Overcrowding is most acute at the high schools, and the district plans to go to split sessions in 2016. Since 2014, voters have rejected three bond issues to bankroll new schools; in May, a $56.1 million bond issue to build a new high school fell 17 votes shy of the needed two-thirds supermajority. On Wednesday, trustees voted to put another bond issue on the Nov. 3 ballot.

Bonneville added 738 students in 2014-15, making it the fastest-growing district in Idaho.

Coeur d’Alene (2014-15 enrollment, 10,450). No hard numbers yet, since classes don’t begin until Tuesday. The district is expecting increases in grade school enrollment and is adding staff, operations and finance director Brian Wallace said. Secondary enrollment is expected to increase slightly, and the district believes it has enough staff on hand.

Twin Falls (2014-15 enrollment, 8,807). Classes opened Aug. 20 to an increase of about 300 students.

That’s a little bit more than expected. Some class sizes will be a little bit larger than the district would like, and elementary schools have added six paraprofessionals to help pick up the slack. “There is no one in the teacher pool at this time,” Superintendent Wiley Dobbs said Tuesday.

The enrollment increase seems to be occurring in the secondary grades. That could be a sign of economic growth, spurred by the Clif Bar and Chobani food manufacturing plants. It might also be a sign that parents are transferring their children from private or charter schools to attend secondary grades.

Trustees approved a $1.3 million emergency levy this week.

Vallivue (2014-15 enrollment, 7,847). The Canyon County district was expecting about 240 additional students. Instead, enrollment is up by about 330. That means the district is looking to hire an additional three or four teachers to ease crowding at the elementary and middle schools, Superintendent Pat Charlton said.

Post Falls (2014-15 enrollment, 5,627). As in neighboring Coeur d’Alene, students in Post Falls won’t return to school until Tuesday. Post Falls might see a 1 percent enrollment increase — and is expecting a slide in kindergarten numbers, Superintendent Jerry Keane said.

Cassia County (2014-15 enrollment, 5,301). Enrollment has increased across the board; as of Friday, the headcount was 5,418.

The bigger problem: The district still has three openings for certified elementary teachers. “We are experiencing an irony of having been able to restore some teaching positions to reduce class size, and now we can’t get the teachers,” spokeswoman Debbie Critchfield said.

Madison (2014-15 enrollment, 5,206). Enrollment is up about 100 students, with most growth in the fifth through ninth grade. Madison Junior High School is adding a portable classroom to accommodate growth, Superintendent Geoffrey Thomas said.