BALTIMORE -- Twenty-five third-graders, all of them boys, were learning to write cursive letters, but the handwriting exercise held other lessons as well. Under teacher Richard Boynton's rules, the class was divided into four tables, and every student at each table had to write the letters perfectly for the table to score.

"Give this table a point," Boynton said, and a half-dozen students erupted in "yeahs" and whirled fists above their heads, in the style of talk show host Arsenio Hall.

Another table did not score because a student literally came up short: Kamian Vaughn's small letter "a" did not reach the middle of the line. Amid "aws" of disappointment, one student slapped the desk, while another got up and stomped his feet. Several peered glumly at the incorrect paper.

When work began on the next word, Vaughn's tablemates coached him as he scribbled it once, erased and tried again. "Come on Kamian, write it good!" Edward Burrell demanded. This time Vaughn did, and his table scored.

"That wasn't too hard to do, was it?" Boynton said to Vaughn. "For the team?"

A rare experiment in public education is underway here at Matthew A. Henson School, where Boynton teaches a classroom of all-black, all-male students. Principal Leah G. Hasty formed the single-sex class last year so that Boynton could be a positive role model for black boys who may come from female-headed households and may know black men only as drug dealers and idlers on the street corners of their impoverished west Baltimore neighborhood.

The school moved tentatively into single-sex education, a tradition brought to this country by European immigrants, as many private schools have gone coeducational to cut costs and comply with parental wishes. Hasty is testing a theory popular among black educators who believe that separating urban black male students can counteract social and environmental factors that undermine their prospects for achievement.

"For black boys, peer pressure doesn't begin when they're teenagers. It starts at six, seven or eight, with their rejection of school," said Spencer Holland, a psychologist who directs the Center for Educating African-American Males, based at Morgan State University here.

Hasty said she decided to try a new approach out of frustration over seeing so many black men idling on the streets near the school. "I thought I might be able to save a handful if I could do something at an early age to give them positive self-images and self-esteem," she said.

While not officially endorsing the idea, the Baltimore school board has tacitly approved separate classes that principals started at Henson, Robert W. Coleman elementary and Paul L. Dunbar middle schools. The only other similar program, according to education officials, is at Public School 137 in Brooklyn, N.Y.

Locally, Boynton's class has not been controversial, but in other cities such as Milwaukee and Detroit that may follow his lead the idea of separate classes or schools for black male students has been criticized as a throwback to the days of racial segregation and sexual inequity.

Critics say they share an interest in improving the academic achievement and social development of black male youngsters, but consider separate schooling inappropriate.

"It's an act of desperation, and I can understand it," said Mary Hatwood Futrell, former president of the National Education Association. "But I would have grave reservations about the experiment. It's not simply black males. What about the other kids who aren't getting a quality education? I don't want black males to feel they have to be treated differently to get a quality education."

The constitutional questions raised by separate schooling are also unresolved. The Education Department advised Dade County, Fla., in 1988 that two black male classes it was planning would violate bans on race and sex discrimination under the Civil Rights Act of 1964. Michael L. Williams, assistant secretary for civil rights, said his office is reviewing the question and may issue a broader opinion.

Boynton's view is pragmatic, not legal. "It's all for the kids. If it works, let's use it, and it seems to be working," he said.

The 557 students at Henson, named for the black man who accompanied Robert E. Peary on his North Pole expedition, were already all black. Hasty said the all-male class receives the same resources and follows the same curriculum as other third-graders. Boynton's boys were randomly selected and include some who had experienced discipline problems.

This is their second year with Boynton, who also taught them in the second grade and moved with them to the third grade -- also something of an innovation. By now, his boys pose fewer discipline problems and have improved their attendance, Hasty said. Half the class did not miss a day of school in September or October.

"That's what I really try to do -- make them want to come to school," Boynton said.

How much impact the class has on academic progress will be evaluated in the spring, when the students take a standardized test. Generally, the boys show enthusiasm for learning -- waving their hands and exclaiming "ooh,ooh" when they want to be called on to answer a question. One boasted aloud as a lesson began: "I'm going to get me an excellent!"

The third grade is particularly important for urban black students, according to educators, because that is when many fall behind, a trend that worsens each year until some lose interest and stop attending.

Boynton, 36, who grew up near the school and attended Bowie State University, said he tries "whatever works" to get through to his students. The handwriting game, he said, was designed to appeal to boys' competitive instincts while teaching teamwork. Putting peer pressure on the side of academics was one result of the game.

"I've used that with coed classes too," said Boynton, whose beard and 6 foot 4 height make him an imposing presence in an elementary school classroom. "But the boys take it to the extreme. I guess you call it 'boy nature.' They want to do better than the other one."

Hasty is undecided about whether Boynton should go farther with the class or let his boys test themselves in a coed classroom next year. Ideally, she said, she would have him take them through the fifth grade, but he doesn't have a teaching certificate to do it.

Holland is in favor of establishing more demonstration classes in the early elementary grades, but is hampered by a shortage of black men who teach those grades. Nationwide, about 18 percent of elementary schoolteachers are men, and a small percentage of them are black.

With his colloquial manner of speaking, Boynton comes across in the classroom as a father figure who regularly imparts lessons about self-control, self-defense and personal appearance. He constantly reinforces his students' sense of maleness, shaking one's hand for answering correctly, addressing another as "Mr. Jerrod" and saying a third "wants to come up here with the big boys in this {faster reading} group."

He also emphasizes reading: A heart-shaped sign above the door reads: "Little girls like little boys who read." On his own time, Boynton takes the class on Saturday outings, including trips to the public library. At school, he sometimes gathers the boys around and reads a story after lunch.

"It's important for them to see a man reading because they'll know you're not a sissy if you read," Hasty said. "We celebrate that he reads to them."

Of Boynton, Michael Kendell, 9, said: "I like the way he works with us, and he's nice." Kendell said he does not miss girls "because they disturb you when you're working and they get their work finished, and you don't."

But Boynton is not always "nice." He sends misbehaving students to a "time-out table" in the back of the room. One recent day, three boys he chastised for not paying attention or not following instructions rubbed their eyes and came near tears.

"It's still not a Garden of Eden," said Boynton. "We don't have a roomful of geniuses. We have a long way to go."