La Cañada school officials on Tuesday formally approved a plan that teachers, parents and students already were acting on: The typical school day this year is six minutes shorter than it was last year, but schools will offer two more days of instruction than they did in the 2011-12 academic year.

In an issue closely watched by parents and teachers, the district scheduled three student-free “collaboration days,” compared to four last term.

Tuesday's unanimous vote formalized calendar adjustments agreed on by the La Cañada Teachers Assn. and the La Cañada Unified School District before the end of the 2011-12 school year.

Formal approval, board member Andrew Blumenfeld said, “just slipped through the cracks” until now.

Last year, the number of instructional days fell to 176 days. Students attended 180 days a year earlier. This year and in 2013-14, students will be in class for 178 days.

Despite the change, the total number of instructional minutes required of certified staff remains the same.

The reduction in collaboration days comes after parents raised concerns that students should not lose instructional time, while teachers said the special days aid students because teachers gain time to hone lesson plans, analyze data and share ideas.

Blumenfeld said research indicates that collaboration days are helpful.

“We surveyed our teachers, and we've had committees of teachers who have looked at the collaboration-days issue,” he said. “On balance, it's a net positive for student achievement.”

Collaboration days for 2012-13 are scheduled for Sept. 28, Feb. 14 and March 15. Tentative dates for 2013-14 are Nov. 1, Feb. 13 and March 14.

The district and the teachers union are in negotiations on a new contract. The previous three-year agreement ended in June.

Blumenfeld said teacher-district negotiations historically “take quite a bit of time,” but added that he hopes they go smoothly.

He doesn't expect negotiations to wrap up before the Nov. 6 election, in which California voters will decide whether to approve two tax initiatives that would boost public school funding.