A Wall Street Journal analysis of high-school Regents test scores shows that a disproportionate percentage of New York City students barely got the passing score they needed to receive a diploma in the past two years, while very few received scores just below passing.

For the 2009 English Regents exams, for instance, students were more than five times as likely to get a 65—the minimum passing grade—than they were to score one point below. In the U.S. History and Government Regents, students were 14 times more likely to get a 65 than one point lower.

"There's no question that there's something fishy going on," said Jonah Rockoff, a professor at Columbia University's business school who frequently analyzes schools-related data sets.

In New York state, high-school teachers score their own students' tests—which differs from tests in most other states, as well as New York's own third- through eighth-grade tests. Mr. Rockoff, who reviewed the Regents data, said, "It looks like teachers are pushing kids over the edge. They are very reluctant to fail a kid who needs just one or two points to pass."

Students at Francis Lewis High School in Queens head to class for the first day of the school year. Ken Maldonado for The Wall Street Journal

Officials from the New York City Department of Education say there is nothing untoward happening. They note that the state actually requires teachers to regrade certain Regents tests where the student barely fails in order to check for grading errors. "All of our teachers are trained on the State's scoring policy before grading the Regents exams, and we're confident the vast majority are adhering to those State guidelines," said Matt Mittenthal, a spokesman for the city's DOE.

Mr. Mittenthal said four of the city's roughly 450 high schools were required last month to conduct their scoring under the supervision of another school because of investigations into their scoring practices.

Some skeptics aren't convinced. Mr. Rockoff points to the eighth-grade math scores in New York City for 2009, which aren't graded by the students' own teachers. There is no similar clustering at the break point for passing the test. He estimates that 3% to 4% of the students who passed the Regents test last year should have failed, based on the DOE data. He said teachers have effectively lowered the passing score on Regents tests to 62 or 63.

A trio of economists—Thomas S. Dee of the University of Virginia, Brian A. Jacob of the University of Michigan and Justin McCrary of the University of California at Berkeley—conducted an independent statistical analysis of the data for the Journal and came to a similar conclusion. They estimated that from 3% to 5% of the students statewide who were given passing grades for the five main Regents exams in June 2009 actually failed the tests. In New York City, between 5% and 10% of students who passed actually failed, they estimated. The three economists have drafted a paper on their findings.

Teachers refer to the practice of lifting test scores as "scrubbing." After teachers grade tests—many times their own students or those of their colleagues—they set aside tests in which the students just missed passing. Teachers say that is generally from 60 to 64, but can go as low as 57. The teachers then ask the original scorer to take another look at the test to see if an argument could be made for giving the student an extra point or more.

Of course, it's perfectly understandable that teachers would help students who are just a few points shy of passing. Students who graduate with scores from a 65 to a 74 must take remedial courses in college anyway, so some teachers reason that helping the student slightly is better than risking that the student drops out of the system altogether.

The integrity of test scores figures into the whole debate over improving school performance. In 2002, Mayor Michael Bloomberg took control of New York City schools. His new school chancellor, Joel Klein, shook things up by introducing autonomy for principals, as well as financial bonuses for performance gains, along with consequences for poor performance. Mr. Klein, who now works for News Corp., the publisher of the Journal, declined to comment for this article.

The New York City graduation rate for 2009 was 59%, up from 46% in 2005, a rate of improvement that far outpaced the rest of the state. The Bloomberg administration has attributed the increase to the new accountability systems that empower principals. Over 45,600 New York City students graduated last year.

Some teachers said the pressure to receive a good grade from the city's Department of Education, which doles out A's through F's based on the number of students passing Regents tests, has driven them to be more generous on the scoring. The DOE has been trying to close schools that get lower grades.

But the concentration around 65s can be seen in other major New York cities, like Albany, Syracuse and Buffalo, where such school-accountability systems don't exist. Looking at past New York City data, Mr. Rockoff said the patterns around the score of 65 were "just as strong in 2000, so it's hard to argue that accountability under Bloomberg and Klein pushed teachers to pass more kids."

Michelle Costa, a high-school math teacher in New York City, said she often hears from friends who teach at other schools who scrub tests, though she doesn't do it. "They are really doing the student a disservice since the student has so obviously not mastered the material," she said. She said it's unfair to students that some teachers do it and others don't.

The Journal analysis included about 1.8 million test scores. For New York City, it received results for two years—2009 and 2010. For the entire state, it received only 2009 data. The data showed which school each score came from, but the identities of the students and their teachers weren't provided by the city or the state.

Some schools have a higher proportion of students getting a 65 than others.

At Sheepshead Bay High School, out of more than 1,100 children who took the U.S. history test last year, 219 got scores from 65 through 68, and only 12 tests were marked with scores from 60 through 64. In the global history exam, out of more than 400 children who took the test, four scored from 60 through 64, while 93 students scored from 65 through 68.

The school's principal, Reesa Levy, dismissed any suggestion that teachers were purposely moving students to a 65. She said she has never heard of the term "scrubbing." She said all of her teachers have been "working harder to get up to 65 this year and push to get up to 75" and are "the strictest graders in the entire world." Ms. Levy said, "To our dismay way too many kids failed the exams and we are working to improve the situation."

The state department of education guidelines for teachers scoring Regents tests say that student papers receiving 60 to 64 in only math or science "must be scored a second time to ensure the accuracy of the score." But the Wall Street Journal analysis shows that test scores appear to be skewed in all of the main subject areas including English and history.

For instance, at Fort Hamilton High School, out of just under 1,000 students who took the U.S. history exam in 2010, none scored from 60 through 64, while 139 scored from 65 through 68. In global history, two scored from 60 through 64, while 280 scored from 65 through 68. JoAnn Chester, the principal of Fort Hamilton, declined to comment.

In New York state, most students must pass five Regents tests—English, math, global history, U.S. history and science—in order to receive a high-school diploma.

In those subjects, Regents exams have a multiple-choice section and also a part for responses such as essays or showing work in math questions. The state provides a rubric for teachers to guide them about when to give a student a point for reaching certain thresholds in their answers.

"Going forward," the state is moving toward an online computer-based testing and scoring system where responses that require teacher judgment would be randomly assigned to teachers across the state, said John King, deputy commissioner at the state department of education. The state is also working on raising graduation requirements, given that the state has determined that even a 65 doesn't indicate students are ready for college.

Concern about grading of Regents tests aren't new. In November of 2009, the Office of the State Comptroller released an audit that concluded that based on a review of June 2005 Regents exams, there was "a significant tendency for local school districts to award full credit on questions requiring scorer judgment even when the exam answers were vague, incomplete, inaccurate or insufficiently detailed. As a result, scores awarded by the local school districts often were higher than the scores determined by the expert review team."

After the audit, the state said it took a series of actions and plans to conduct annual "spike/cluster analysis of scores to identify schools with suspicious results."

Write to Barbara Martinez at Barbara.Martinez@wsj.com and Tom McGinty at tom.mcginty@wsj.com