Yap Zong Yao woke up at 5 a.m. Saturday in Singapore to check his admissions decision from Vassar College. He returned to sleep "overwhelmed with joy," he said.

Mahmoud Ghedira stayed up with family members until 11 p.m. Friday in Tunisia as they toasted the son who had impressed an esteemed American school.

Megan Curiel, from San Antonio, saw the good news on her iPhone and sobbed. Her father called relatives. She ordered two Vassar sweatshirts — one for her and one for her mother. They popped Champagne.

"I was in," Curiel said, "for about three hours."

About 4 p.m. Friday, Eastern time, scores of early-decision applicants to the college, in Poughkeepsie, N.Y., were mistakenly told they had been accepted, the school said.

Jeff Kosmacher, a spokesman for Vassar, said on Saturday that a "test letter" that had been intended as a placeholder for the real admissions decision had not been replaced before students checked their application statuses online. The error was discovered around 4:30 p.m., he said.

Between 6:30 and 7 p.m. Friday, the 122 students who had seen the test letter — 46 who were, in fact, accepted and 76 who were not — were sent a message from the college that cited a "system error" and apologized for the mistake, Kosmacher said. The correct decisions, the message said, were now available online.

"If after checking your decision again you still have questions," the message said, "please feel free to contact the Admissions Office on Monday morning."

Though some parents have requested refunds of application fees, Kosmacher said that besides Friday’s message, "no other step is in the works." A total of 254 students had applied for this round of binding early decisions, he added, and some had logged in while the error was online.

Word spread quickly among the applicants, many of whom had been communicating on the website College Confidential in the days before the decisions were to be released, sharing their well-wishes and trepidation.

Curiel heard from a classmate who had also been told he was accepted. Ghedira found out early Saturday morning. "He was so happy, he wanted to read it again," his mother, Sonia Ghedira, said Saturday, adding that her son was too distraught to come to the telephone.

At 5:11 p.m. Friday, the first panicked message hit the College Confidential message board: "Now it says I’m declined??????"

"Accepted at 4, reject at 5," read another. "I don’t understand."

Some students and parents tried to contact the Admissions Office, demanding further explanation. The parents of one student in Connecticut who was rejected said they were considering legal action because the decision was supposed to be binding.

Other applicants began the unpleasant work of contacting friends and relatives anew.

"My mom called, like, my entire family," Dylan Leggio, 17, a student at Somers High School in Westchester County, said in an email. "It was just a big letdown."

Curiel said she felt an obligation to correct the record with loved ones as soon as possible. "I told everybody I got into Vassar," she said. "I would be lying."

Curiel added that she nearly caused herself an even greater headache by withdrawing her other applications because the Vassar decision was binding.

"Take care of this tomorrow," she recalled her father saying. "Right now we can celebrate."

Vassar is not the first college to supply false hope to students. In March, 61 applicants to the University of Delaware received misguided congratulations. Similar errors have plagued the University of California, San Diego, and the University of North Carolina at Chapel Hill in recent years.

For some students, Vassar’s mistake brought a moment of clarity. Posting on the College Confidential thread, Leggio mused that perhaps he preferred a school in a city after all.

Kareen Troussard, a student in Paris, said the episode might have saved her. "I want to major in computer science," she said in an email, "and Vassar doesn’t even know how to use a computer on the biggest day of our lives."