The Seattle School Board has approved a $689 million general-fund budget for the coming school year — about 8 percent more than last year, mostly because of increasing enrollment, according to the district.

About 1,300 more students are expected next year, boosting total enrollment to more than 52,000 in 97 schools.

The district, which employs about 8,000, is adding 122 teachers, 130 teaching assistants and other staff including counselors, psychologists and nurses.

The administration had anticipated an $18 million shortfall, but made up the difference with an unexpected increase in funding from the state, savings in bus transportation, and work with the teachers union to find additional money in the budget.

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School Board actions in recent weeks required some last-minute budget tweaking.

Last month the board chose new math books for the district’s 28,000 elementary- school students that initially appeared to be twice as expensive as the books favored by an advisory committee that compared the options.

District staff said the board’s choice — Math in Focus, an American version of Singapore’s national math curriculum — would cost about $8 million over seven years with first-year costs of $3 million.

About $1 million of that difference is because Math in Focus will require four days of teacher training instead of one day for the books recommended by the advisory committee, according to the district.

But after further negotiation with the vendor, the district brought the overall price for Math in Focus down to about $6.6 million and lowered the first-year expenses to about $1.3  million by spreading out the total cost more evenly across the seven years.

On Wednesday, the same night the board adopted the budget, it also directed the staff to engage in a 15-month study to change school starting times.

Several area sleep experts have joined parent activists in calling for school schedules that accommodate teens’ biological sleep patterns, citing research that later start times for adolescents improve health, safety and academic achievement.

But the change likely would have far-reaching consequences affecting elementary-school students and the timing of athletics, before- and after-school programs and other functions.

The staff estimates that such a study would require the equivalent of six full-time, dedicated employees, three of whom could be hired from outside the district, plus polling costs and other expenses.

The new budget sets aside $571,000 for the study.

John Higgins: 206-464-3145 or jhiggins@seattletimes.com On Twitter @jhigginsST