For most students, the first day of school symbolizes the promise of new beginnings. Some vow to work harder, try for better grades or get more involved in extracurriculars.

But at Gaithersburg High School, the start of the school year Monday took on additional meaning as more than 2,000 students walked into a new, state-of-the-art building a decade in the making.

“I could not wait,” said Damani Wardrick, a 17-year-old junior. “It means a fresh start.”

More than 151,000 students returned to school in Montgomery County on Monday. The school system marked the new academic year with the highest student enrollment in the county’s history and four modernized and expanded school buildings.

While Glenallan Elementary School, Weller Road Elementary School and Herbert Hoover Middle School saw campus improvements this year, the new building was particularly meaningful at Gaithersburg, the county’s second-oldest high school.

The $95.8 million Gaithersburg project replaces a 62-year-old building, which will be torn down during the coming year.

Gaithersburg Principal Christine Handy-Collins said she has been working on expansion plans for about six years.

“It is exciting to see what you plan come to fruition,” Handy-Collins said. “When you have a brand-new, 21st-century school open in your community, you can’t help but be excited.”

The high school’s expansion reflects the need for more classroom space countywide. This is the 30th year of growth for Montgomery County’s school system and the first time enrollment has exceeded 150,000. An estimated 2,500 new students filed into classrooms Monday, and district officials predict student enrollment will swell to more than 159,000 by 2018.

To accommodate the rising number of students, Montgomery finished a dozen major construction projects over the summer, adding 83 new classrooms.

But beyond new buildings and bigger enrollment, the new school year marks other changes in Montgomery County.

Montgomery welcomed 800 new teachers to the district and dozens of new principals.

And classroom instruction also will continue to change as Curriculum 2.0 expands to fourth and fifth grades this year. Montgomery County has been rolling out Curriculum 2.0 to align instruction with Common Core, new national education standards aimed at being more challenging for students to prepare them for college and careers after high school.

Curriculum 2.0 launched in kindergarten through third grade last year and has raised complaints from some parents, who worry that the material doesn’t challenge brighter students, particularly in math. Parents have also said that new report cards aligned to Curriculum 2.0 are confusing, without clear ways of knowing how students can earn top marks in a system that doesn’t use a traditional A through F scale.

This is also the first year Montgomery will launch several new efforts aimed at closing the county’s persistent achievement gap — as white and Asian students have been performing better academically than the county’s black and Hispanic students. One of the new efforts includes monitoring first-grade students for early signs that might indicate a likelihood they might later drop out of school. Another initiative will provide intense, individualized coaching to 10 “innovation schools.”

The excitement at Gaithersburg started at about 6 a.m. Students arrived early, giving themselves extra time to explore the building and chatter in the halls. Under the archway of the main entrance, the cheerleading team and the marching band, decked out in royal blue and gold, greeted students before the first bell rang.

Assistant Principal Susan Frishman shared the students’ excitement, dancing with the Trojan cheerleaders.

“I feel like crying,” said Frishman, who is starting her sixth year at Gaithersburg. “It is just so amazing to see kids so excited to come to a new place.”

Students and parents marveled at the new technology in the classrooms and the natural light pouring into the school. Many of the classrooms in the old Gaithersburg High School didn’t have windows.

“The air just feels so clean and clear,” said Carrie Bohrer, a Gaithersburg parent who was also a teacher and student at the school. “And everyone is amazed at its immensity.”

The renovation adds more than 108,000 square feet of space — equivalent to almost two football fields.

While the first day of school brought change and a fresh start for some, the transition might be more difficult for others.

Ray Lewis, a building services employee at Gaithersburg, has been working at the school for 42 years. When Handy-Collins asked him about the new building and shiny facilities Monday morning, he responded: “It feels weird to me. I need to get used to it.”