Classes begin Tuesday in Montgomery County, the state’s largest school system, following a state mandate that schools open after Labor Day. (Bill O'Leary/The Washington Post)

More than 160,000 students headed back to school Tuesday in Montgomery County as the sprawling suburban district outside Washington projected another year of record enrollment and deepened its focus on foreign languages and career education.

The first day of classes in Maryland’s largest school system arrived later than it has in more than a decade, after a new state mandate that schools open after Labor Day. But much was otherwise the same, with teachers across the district’s 205 schools welcoming backpack-toting students.

Neighboring Prince George’s County opens schools Wednesday, projecting a fifth year of rising enrollment, with more than 132,000 students. In Northern Virginia, classes resumed Tuesday in Arlington and Alexandria, following earlier openings in other Virginia school systems and in D.C. Public Schools.

Montgomery County Superintendent Jack Smith started the day before sunrise at Paint Branch High School in Burtonsville, where he mingled with students in hallways and talked to one class about overcoming the jitters and seizing the potential of high school.

“This is the most important time to be curious,” he said.

Smith, starting his second year as the district’s leader, said in an interview he would like to see evidence of greater learning across grades and student populations in the year ahead, and an increased awareness of career opportunities.

Montgomery is increasingly diverse — roughly 30 percent Hispanic, 29 percent white, 22 percent black and 14 percent Asian — with more English-language learners and economically disadvantaged students in recent years.

“Every single student needs to walk out well-prepared for college, well-prepared for career, or well-prepared for both,” he said.

Nearly 1,000 new teachers are joining the Montgomery school system this year, and new Spanish-English language immersion programs began at Brown Station Elementary and Washington Grove Elementary. More than 100 new school buses are on the road.

This year’s expected jump in enrollment — by nearly 2,300 students, to 161,302 — would mark the ninth consecutive year that the high-performing county school system has recorded a yearly increase of more than 2,000 students.

“It’s going to continue to be a challenge for us, facility-wise and resource-wise,” school board member Patricia O’Neill said.

Montgomery’s enrollment surge of recent years is driven by birthrate trends and a continuing influx of families, said school district demographer Joel Gallihue. Existing neighborhoods are turning over and bringing in more parents with young children. During four of the past five years, sales of existing homes increased, he said.

Smith began the new school year with a vote of confidence from the board of education, which last week boosted his salary by $15,000, to $290,000 a year. That makes his pay comparable with his counterpart in Fairfax County, Va., according to a district analysis.

“Montgomery County Public Schools is the 17th-largest school system in the nation, and we want to make sure we remain competitive,” said Board of Education President Michael Durso, noting that the pay increase was initiated by the board.

The county opened a new school this year — Silver Creek Middle in Kensington, its 205th — and completed a classroom addition at Diamond Elementary in Gaithersburg. Students are attending newly rebuilt schools at Brown Station Elementary in Gaithersburg, Wayside Elementary in Potomac and Wheaton Woods Elementary in Rockville.

Shortly after he stepped into the top post, Smith cited the narrowing of achievement gaps as “a moral imperative for the community.” The system’s high level of success would not continue without doing more for students of color, those in poverty, English-language learners and children in special education, he said.

On Tuesday, Smith echoed those remarks and said the school system had made progress by increasing access to rigorous coursework. More Hispanic and black students took Algebra 1 in eighth grade, for example, he said. “If you don’t have access to the concepts, the material, the information, you cannot be successful in it,” he said.

In Prince George’s County, the state’s second-largest school system, educators held student orientation Tuesday for ninth-graders and those transitioning to middle school.

To mark the opening of the school year in Prince George’s, the system’s chief executive, Kevin Maxwell, plans to make stops at several schools Wednesday, including a new $93.7 millioncampus for Fairmont Heights High.

“We will provide new facilities, new programs and more opportunities for young people to be successful in life,” Maxwell said.

He also is scheduled to visit Charles H. Flowers High, which has a new program that offers students a path to a bachelor’s degree for $10,000 or less, and Frederick Douglass High, which has a program that places students in line for jobs in the health-care and hospitality industries.

Student safety issues have sparked concern in Montgomery and Prince George’s during recent years.

In March, the Montgomery school system drew national attention as two immigrant students who had crossed the border illegally were accused of raping a fellow student inside a bathroom stall at Rockville High School. Prosecutors eventually dropped all sex-assault charges in the case.

But parents and others raised questions about school security, and Smith launched a school-by-school security review. The district recently completed an examination of its 25 high schools and is making upgrades and changes.

In June, a longtime Montgomery teacher was convicted on sexual abuse charges, raising questions about how the school system handles incidents of inappropriate conduct.