After new school and bus schedules caused upheaval at the beginning of the school year, the Portland school district is changing the morning bell times this fall for some elementary and middle schools.

The changes “are designed to ensure that buses are waiting when students are dismissed from school and that buses won’t arrive at school more than 15 minutes before school starts in the morning,” said a news release from the Portland Public Schools.

The district grappled with problems over the bus schedule earlier this year, after parents complained that buses arrived at schools before staff was there or long after the final bell.

The problems mostly affected elementary schools, which are divided into two groups and started 20 minutes apart. That caused logistical problems because it didn’t give the district’s yellow buses enough time to make the runs.

Under the changes, there will be the following new start and end times for the 2016-17 school year:

• Lincoln and Lyman Moore middle schools will start 10 minutes earlier, going from 7:45 a.m. to 2:15 p.m.

• East End Community School will start 30 minutes earlier: 8:10 a.m. to 2:50 p.m.

• Longfellow Elementary School will start 20 minutes earlier: 8:20 a.m. to 2:50 p.m.

• Presumpscot Elementary School will start 10 minutes earlier: 8:30 a.m. to 3 p.m.

• Ocean Avenue Elementary School will start 10 minutes later: 8:30 a.m. to 3 p.m.

• Hall, Reiche and Lyseth elementary schools will start 20 minutes later: 9 a.m. to 3:30 p.m.

• Bayside Learning Center will start 50 minutes earlier: 7:30 a.m. to 1:40 p.m.

There will be no changes to the high schools, the Portland Arts and Technology High School, King Middle School, Riverton Elementary School or the island schools on Peaks and Cliff islands.

The school board approved the new start times for the 2015-16 year as part of a larger initiative to add 20 minutes to the school day, and switch all high school students off the yellow buses and onto Metro buses.

CORRECTION: This story was updated at 10:54 a.m. on May 18, 2016 to clarify the start time for Ocean Avenue Elementary School.