Niskayuna High School was placed in lockdown at around 1 p.m. Monday, after a student found a threatening note, the school said in a message posted on its website.
The lockdown delayed dismissal into the evening and prompted all after-school activities at both the high school and middle schools to be canceled, the district said.
A thorough search of the school found nothing connected to the threatening note, the district said. Classes were expected to resume as normal Tuesday.
An update that was posted to the district website at 6:30 p.m. indicated the school had been fully checked and dismissal procedures had begun. The dismissal process itself might take some time, the district wrote.
"We again thank everyone for their patience and cooperation, and thank the Niskayuna Police Department and several area agencies for their work today and ongoing partnership," the district wrote.
The 6:30 p.m. update was accompanied by a letter from Principal John Rickert.
"The school district and police undertook the precautions and procedures necessary to investigate the threat that was brought to our attention," Rickert wrote. "However, we know this was not easy day for students and we will do everything we can to support them."
The criminal investigation continued, Rickert said, but police have assured the district that classes can resume as normal Tuesday. Counselors and social workers are to be on hand for any student who wants to talk about the situation, he said.
"We will make Tuesday as normal as possible for students, while also providing support as needed," Rickert wrote.
A review of the response is expected to be undertaken, as would be in any similar situation, Rickert wrote. The district's safety committee is set to meet this week and a debriefing on the lockdown will be on the agenda.
"Following that meeting, there will be a public forum to discuss this situation. We will let you know when that is scheduled," Rickert wrote.
The district's updates and Rickert's letter: Niskayuna Central Schools
The district gave multiple updates on the situation through its website. Earlier updates noted the ongoing searches and reminded parents not to come to campus during the lockdown.
"We understand that this is a frustrating situation, and we thank you for your patience and cooperation," the district wrote in an earlier update.
The lockdown comes a week after a Niskayuna student was arrested on charges of making a terroristic threat against the school, using social media.
Threatening notes have also prompted at least two lockdowns at Iroquois Middle School, where, after one lockdown, school dismissal had to be delayed.