When an infraction occurs - plagiarism, for example - the honor board, in part made up of students, hears the case.
Nearby Haverford College has a similar code and student self-governance, and conducts exams in much the same way.
"It's funny because now I'm a senior and I almost forget that it's there," said Lucia Kearney, 21, of Swarthmore , "because everybody actually follows it. I don't know of anyone who has ever cheated."
Students at Princeton University also take exams under the school's honor code.
"Examinations are not supervised," Princeton spokesman Martin Mbugua said. "On each examination paper, the student writes out and signs the following statement: 'I pledge my honor that I have not violated the Honor Code during this examination.' "
Honor codes in the sense that they are used at Haverford, Bryn Mawr, and Princeton are relatively uncommon in higher education, according to Donald McCabe, a professor of management and global business at Rutgers University. McCabe, who has studied cheating, estimates that fewer than 100 schools around the country have such codes.
He said the codes typically feature one or more of four aspects: Exams that are not proctored, pledges that students must sign saying they didn't cheat, judiciary or honor boards evenly or largely made up of students, and a requirement that students confront and report violators.
"Schools have not made it a high-enough priority in my view," McCabe said. "In no place [within a curriculum] are we trying to educate students concerning ethical responsibilities."
After students were accused of collaborating on a take-home exam at Harvard University this year, the university said it would consider an honor code, though no decision has been made, a spokesman said this week.
Several local schools said that although they do not have honor codes, they have codes of conduct or other policies that set standards.
Student buy-in and involvement are key to an honor code's success, said Ronald L. Dufresne, associate professor of management at St. Joseph's University.
The relatively small size of Bryn Mawr and Haverford - Bryn Mawr has about 1,300 students, Haverford 1,200 - is an ideal environment for an honor code, he said.
"The real underlying dynamic is the strength of the student culture," DuFresne said. "It's easier to have a strong student culture at a small campus."
The roots of the codes at Haverford and Bryn Mawr date to the 19th century. The codes have been periodically updated, and, in a sense, grew up with the institutions. It's much more difficult to adopt a code that tries to change a culture, DuFresne said.
"The honor code is part of the fabric of what it is to be a Bryn Mawr student," said Michele Rasmussen, dean of the undergraduate college, who also serves on the honor board.
Rasmussen, who was previously at Duke, which had no honor code, said she was skeptical of the process at first.
"This whole notion of student self-governance was totally new to me," said Rasmussen, in her third year at Bryn Mawr.
But it works, with guidance and advice from adults as needed, she said.
At Haverford and Bryn Mawr, the honor boards' actions against student violators are more educational than punitive.
"It's how can the community help you," said Tong, an honor board member from Durham, N.H. "There's this mutual healing that happens."
Actions can range from requiring a student to write a letter of apology to a professor to suspension from campus for a semester or more. At Bryn Mawr, all suspensions automatically go to the president's office for review.
The school suspends on average two or three students a year, Rasmussen said.
Both schools say most violations are minor, such as inadvertent plagiarism through sloppiness or lack of appropriate citation.
At both schools, serious matters involving health and safety, such as sexual assault, are handled by the dean's office.
Student interactions involving minor social issues, such as leaving hair in the bathroom drain, are governed by the code, though they seldom go to a hearing.
Both schools report relatively few code violations.
At Bryn Mawr, the board dealt with two cases this semester, both holdovers from spring. There have been as many as eight cases in a semester, Rasmussen said.
Haverford has about five cases that go to a hearing per semester. Each can take hours, said sophomore Tamar Hoffman, 18, honor council cochair.
"It's hard sometimes to decide what's in the best interest of the student and the community," said Hoffman, of Tel Aviv.
The honor council meets once a week, partly in public, to discuss community issues such as the increasing availability of information on the Internet and its implication in the context of plagiarism - and then in private on cases.
The council also focuses on education.
Last week, Hoffman toted a backpack full of signs she planned to post around campus dorms, academic centers, and the library, reminding students about exam week rules.
"Please do not discuss the form, content, and degree of difficulty of exams!" the signs read.
There are some key differences between Haverford's and Bryn Mawr's codes. Haverford's council is exclusively students and its code requires students to confront and report classmates if they witness a violation. At Bryn Mawr, students aren't required to report.
Bryn Mawr discourages take-home exams; Haverford does not, Rasmussen said.
At both schools, students learn about the codes when they enroll. At Haverford, students aren't required to submit a deposit for admission; their word is good enough.
"It's really a way of life," said Martha Denney, Haverford's dean of the college.
Haverford senior Jacob Horn, 21, of Washington, said the code bonds the community: "It affects the relationships you have with the professors, the relationships you have with your peers. You trust everyone."
Contact Susan Snyder at 215-854-4693, firstname.lastname@example.org, or follow on Twitter @ssnyderinq.