The first week of school for students in Suffolk’s public schools is over, and some classrooms are a little more crowded than expected.

More than 400 students were in school on the third day than had been pre-registered, school officials said.

On Tuesday, Bethanne Bradshaw, spokesperson for the school system, reported that 13,812 students had pre-registered and were expected for the first day of school. According to a report on Thursday by Interim Superintendent Deran Whitney, attendance records showed 14,222 students in the classrooms on Thursday.

“We have more students than we had expected, and we’ve increased from last year,” he said. “We did not anticipate this much growth, but we are prepared to handle it.”

Attendance on the first day of school tallied at 13,648 and jumped by more than 300 students on Wednesday to 14,080, according to Bradshaw.

At 14,222 students, there are at least three classes in the elementary schools that are over — “well over” — capacity, a situation that would require moving faculty around to accommodate the growth, according to Whitney.

In addition to a number of students who did not pre-register for classes, with an attendance of 14,222 students, the school system has grown by 183 students over last year, which itself had been a growth year, with 240 students more than the previous school year.

While the administration prepares for the students who haven’t pre-registered, growth in the schools is a new trend, according to Whitney.

“Before last year, the most we grew in the preceding three years was 56 students,” he said.

Before any changes are made, however, there is a 10-day waiting period from the first day of school.

“It takes at least 10 days for schools to determine exactly how many students we expect to attend through the year,” Whitney said. “We always start school the weekend after Labor Day, and we don’t always get all our students until the following week. After that time period, we’ll address the student-teacher ratios and add teachers and sections as needed.”