Prince George’s County Executive Rushern L. Baker III (D) gained authority to reshape his county’s school governance this year, and he spent the past few months assembling the team he hopes can help turn around the struggling school system.

But it wasn’t until the first day of school Monday, when more than 120,000 students streamed into their classrooms, that Prince George’s actually stepped into the new era. It is one that Baker hopes will bring major improvements to the county’s educational landscape, one that he believes will transform one of Maryland’s lowest-performing school districts into a system that could help raise the county’s profile.

“This is a new day and a new opportunity,” schools chief executive Kevin M. Maxwell said as parents, some with cameras in hand, ushered their children into Bladensburg Elementary School.

Kayla Jones, a fourth-grader at Bladensburg Elementary, clutched a pink-and-purple insulated lunch bag while carrying a backpack full of composition paper and notebooks. Tricy Jones, Kayla’s mother, asked, “Are you excited?”

Kayla nervously smiled and said, “Yes.”

Maryland Gov. Martin O’Malley (D), who joined Baker and Maxwell on Monday as they welcomed back students at Barnaby Manor Elementary School and the newly built Oxon Hill High School, said expectations are high.

“These can be some of the best years for Prince George’s County schools,” O’Malley said, describing Maxwell as “one of the best in the country” to lead a school district.

It was Maxwell’s first opening day at the helm of the school system from which he graduated. He left the Anne Arundel County superintendent’s job this summer to join Baker’s effort.

Segun Eubanks, who was appointed by Baker as chairman of the county’s revamped Board of Education, shared in the excitement of what he sees ahead for the school system, the largest in the Washington area to open Monday. Public schools reopen next week in the District and Anne Arundel, Montgomery, Howard and Charles counties. School starts in Northern Virginia on Sept. 3, after Labor Day.

“We’ve experienced progress for the past five years, but now we have a new CEO, a newly reconfigured board and a county executive that is all in,” Eubanks said. “Now we can put initiatives in place and work together to see the accelerated growth that we need to become a top-performing district.”

In March, Baker jockeyed for a complete takeover of the school system, one that would give him control over the schools chief and the school system’s $1.7 billion budget. Under a compromise, the county executive was given the authority to select the system’s chief executive and add new members to the school board. The budget remains under the board’s control.

Jusalyn Smith, who is affectionately known as “Granny” at Bladensburg Elementary School, where she volunteers, said she is optimistic about the county’s future.

“I hope everything will come together and the kids will get the activities that they need,” Smith said as she dropped off her grandchildren, fifth-graders Andrea Smith and Crya Kearny.

Maxwell, the eighth schools chief in Prince George’s in 14 years, said he was restless Sunday night. It’s the same feeling he’s had the night before every first day of school since he became an educator 35 years ago.

“It’s that sense of opportunity that awaits,” he said.

Maxwell acknowledged the challenges ahead, which are far different from the ones he faced when he was a teacher and a principal in Prince George’s.

Maxwell has said he plans to take a hard look at the county schools’ allocation of resources, classroom sizes and instruction. He wants to focus on accelerating academic achievement and luring middle-class parents — many of whom have removed their children from the county’s schools in favor of private schools or other jurisdictions — back to the public school system.

“There is a lot riding on it,” Maxwell said of the overhaul in Prince George’s. “But I’ve always been focused on the success of schools. The outcomes are still about children and about fulfilling their hopes and dreams.”

Unlike previous years in Prince George’s, when buses failed to arrive on the first day or thousands of students did not have class schedules, there were few problems at schools in the county Monday.

But there was at least one glitch.

At Eleanor Roosevelt High School in Greenbelt, the premier county high school, students returned to find no lockers in the hallways. School officials said they would not issue textbooks until the lockers are installed, instead giving out alternative assignments. The lockers are expected to arrive by next Monday.

Max Pugh, a spokesman for the school system, said the school has sent a letter to parents saying that the lockers were not replaced because of a problem with the manufacturer.

County Council member Mary A. Lehman (D-Laurel), whose daughter is a junior at Roosevelt, said she hopes the locker problem is not indicative of larger concerns.

“This is a classic example of a job that should have been done over the summer,” Lehman said. “School begins with high school kids with no lockers, and the way the school system deals with it is not issuing textbooks. We have to do better. It’s frustrating. People cannot treat situations like this as if they are normal, because they are not.”

She said she realizes Maxwell just arrived weeks ago, and she remains optimistic that things will change. Last year, Lehman’s daughter’s bus struggled to arrive at school before the end of her first-period class, causing students to miss important instructional time.

“I’m hopeful, but he’s definitely got his hands full, there’s no doubt about that,” Lehman said. “I am still hopeful, but clearly things have to be done differently.”

John Wagner contributed to this report.