School started in Prince George’s County on Monday August, 20, 2012. Students arrive to their first day of classes at Greenbelt Middle School. (Sarah L. Voisin/WASHINGTON POST)

The eighth-grader was jittery. “The butterflies are in my stomach,” said Tatiana Jimenez as she waited outside Greenbelt Middle School on Monday morning with her mom for the first day of school.

One of Tatiana’s worries was getting the classes she wanted (art was a top priority). Another was navigating her way around a new two-story building.

For this 14-year-old and her Prince George’s County schoolmates, part of the first wave in the Washington region to head back to school, there was even more change in store: They will be spending an additional 40 minutes a day in school this year as part of the latest plan in Maryland’s second-largest system to raise academic achievement.

Most middle school students in the county will receive additional help in science, math or reading. Some who don’t need remedial instruction will get an equal amount of enrichment time in subjects such as music or a foreign language.

“This is the make-it-or-break-it time for most students,” said Robin Keys, who teaches seventh- and eighth-grade science at Greenbelt Middle. “If they don’t have a strong foundation from middle school . . . we’ve lost them.”

A. Duane Arbogast, the deputy superintendent for academics, said middle school is a time of substantial transition for students — physically, emotionally and intellectually. “It can be a disconcerting time for kids,” he said.

The county has placed a greater emphasis on middle schools this year by lengthening the school day of most and, in the Greenbelt community’s case, using public funds to build a $56 million state-of-the-art building. The new building, on a 32-acre campus, is outfitted with technological gear such as interactive whiteboards and has an environmentally sensitive design. It replaces one of the school system’s oldest facilities.

“We have made great progress in our elementary and high schools with the type of special programs that are offered there,” said County Council Chairwoman Ingrid Turner (D-Bowie), who attended the Greenbelt Middle opening. “But [middle schools are] where we need to boost up our math and reading.” The county’s eighth-grade test results in those subjects trail the state average by a significant margin.

Tatiana was one of more than 120,000 students who returned to class Monday in Prince George’s, the first school system in the Washington region to reopen after summer break.

“Students came to school today ready to learn, thanks to our outstanding faculty, staff and parents,” said Board of Education Chairwoman Verjeana Jacobs (District 5). “In dealing with all of the moving parts that a new school year brings, parents have been patient and flexible. We are pleased that the school year got off to a smooth start and look forward to a great year.”

Schools will reopen Tuesday in Calvert County and Wednesday in St. Mary’s County.

School starts next week for the D.C. Public Schools system and the systems in Anne Arundel, Montgomery, Loudoun, Howard, Charles and Frederick counties. Starting dates vary among D.C. public charter schools, but most open this month.

In most of Northern Virginia — with Loudoun a notable exception — school starts Sept. 4.

The school year in Prince George’s is opening with new leadership. Last week, the county Board of Education announced that it selected Alvin Crawley, a former D.C. school official, as interim replacement for outgoing Superintendent William R. Hite Jr., who was recently named Philadelphia schools chief. Crawley begins Sept. 4.

At Greenbelt Middle, where 1,050 students are enrolled, Tatiana wasn’t the only antsy student. The gymnasium was filled with hundreds of them as they waited for their schedules and compared notes with friends.

“I couldn’t sleep last night, I was so excited,” Kobe Broadwater, a sixth-grader, said as he began his first day of school. “It’s a new building, a new gym.”

Kobe said he kept thinking: “I’m going to middle school — finally.”

Meanwhile, Tatiana wondered when she would finally get to go to her middle school classes.

An hour after arriving at school, she sat anxiously on a black folding chair in the gymnasium while her classmates received their schedules and left her and about 70 other students behind. She started rubbing her hands and cracking her knuckles. “I’m surprised I’m not biting my nails,” she said.

A few minutes later, Tatiana grabbed her black-white-and-purple-checkered backpack and picked up her schedule from the counselors at the table and headed to Room 1201 for math class.

“I got art,” she said, showing off her schedule and a mouth full of braces to a friend.

But the schedule is temporary. School officials said Tatiana and dozens of other students will learn Tuesday about their permanent schedules.

“We had some scheduling glitches, and we’re working on them,” said the school’s principal, Warren Tweedy.