The hallways were busy at Phoenixville High School in Chester County, as students learned their new schedules and saw friends again.
The district started a full week earlier than it usually does this year. Officials say this will make for a longer summer next year to accommodate a new school that's being built.
"I was nervous, but it's going well," said Keira Hesnan, a senior.
"I'm kind of nervous essentially about my schedule and figuring out where all my classes are," said Sophia Puleo, a senior.
Both Phoenixville High School seniors are enrolled in a special program for students interested in becoming teachers.
So, they will have many more first days in the years to come. Their teacher said she still gets butterflies on the first day back.
"Anxious to come back and see them," said Brittney Ehrenzeller, a teacher at the high school.
"Some of them I've had before, so it's great to see them and see them excited," she added.
Despite Monday only being Day 1, many are already thinking about the last day of the academic year.
"When I think about college, I usually cry. It's really scary," one senior told Action News.
Philadelphia starts school on Monday, August 26. Many other schools will have the first day of school after Labor Day.