Aaron Stitt, 16, considered himself one of the tough guys. A chronic truant who failed eighth grade twice, he said he would think nothing of cursing out his D.C. public school teachers.

But when he walked into the quiet halls of the Holy Redeemer School in Northwest Washington last month for summer classes and confronted an array of religious statues and the stern, bearded face of Brother Patrick McCarthy, he thought to himself, "What am I doing in this place?

"You got to line up for class and you can't get a drink of water when you want it," Aaron remembers complaining to his public school friends in those first days. "Then, in class, I saw they was helping me, and I said, 'Hey, I like this.'"

Aaron, a student from Terrell Junior High School, could only add and subtract whole numbers when he came to this Catholic school's six-week summer program. Now, he can add, subtract, multiply and divide fractions and decimals as well.

Aaron used to identify words like injured and weak as nouns, although they were used as a verb and an adjective in a sentence in a test question. As a result, he got big red Fs on his earliest English assignments for errors like that and for writing sentences like, "Me and Joe are going to play pinball." Aaron, who scored 21 on his first grammar test in the summer session, got a 97 on his most recent test, which dealt with some of the same material.

Because of his progress this summer, Aaron and his grandmother have agreed that he will attend eighth grade at Holy Redeemer in the fall.

McCarthy and the other teachers at Holy Redeemer say Aaron always has had the ability to do the work, but what he lacked -- and needed -- was a highly structured, disciplined and secure classroom atmosphere. It is this emphasis on structure and discipline, they believe, that has made Holy Redeemer's summer school one of the fastest-growing and most successful in the city.

Such private school programs also are becoming a necessity in the city since the public schools have had to limit their summer school program for the second straight year because of budget cuts. Only 900 students are enrolled in the public school summer program, those who failed one or two courses needed to graduate from high school or graduate from ninth grade into high school.

Another 2,700 students in grades one through three are in a special tutoring program, paid for with a $2.8 million grant from the Department of Employment Services. Under that program, 2,700 junior and senior high students in the city's summer jobs program tutor students who failed to be promoted in June under the system's new standards for promotion under which they must master specific skills in reading and math. f

Holy Redeemer, which is located at 200 New York Ave. NW, near a group of rundown row houses, takes most of its 118 summer students from neighboring public schools, Walker-Jones Elementary and Terrell Junior High. Many of the students are referred to Holy Redeemer by their public schools teachers or counselors.

The students pay only a $5 registration fee. All of the teachers volunteer their time.

The test scores of the students in the program show its high rate of success: The same students who scored as low as 23 or 32 out of 100 or reading tests when they first came into the program in June scored 78 and 83 by the end of the program last week.

Students who were reading on a fourth- or fifth-grade level in their junior high school are reading John Steinbeck's The Pearl , a book used in junior and senior high, and understanding it.

Only seven of the 118 students in the program did not progress enough to pass onto the next grade in September.

"I'm just so happy I don't know what to do," Aaron's grandmother, Annie Crutchfield, said of his school work this summer. "I saw more progress in Aaron in six weeks than I did in the past two years."

How can a six-week summer program help students make significant strides? Father J. Richard Griffin, pastor of Holy Redeemer and creator of the summer school, says the success starts first with having high expectations of the students.

"What I feel is wrong with the public schools is that the teachers don't have authority. . . . The children are handed a bill of rights. It's as if the children are running the schools," Griffin said. "Here at Holy Redeemer, we have very high and difficult expectations for each child."

The first thing students are expected to do is to listen and follow directions. When the first bell of the day rings, the students -- many of whom have had discipline problems in their own schools -- drop their basketballs or whatever else they are playing with and stand silent.

Then McCarthy raises his hand -- the signal for the second bell to be rung -- and the students form an orderly single-file line and move silently to their classrooms.

"That type of thing sets the tone for the whole day," said Griffin, a 40ish pastor who, despite his no-nonsense educational philosophy, speaks with warmth of every student.

In class, the teachers try constantly to get the students to systematize their school work as a way of teaching them to "put order in their lives," McCarthy explained.

"I am constantly asking them to copy things off the blackboard to get them used to writing whole sentences and putting things in order," he said. "I have found that a lot of the students were used to just being handed a mimeographed sheet, a paper where all they had to do was fill in the blank. They were not used to writing complete sentences."

Those who will not follow directions in class or need extra help, McCarthy said, are expected to attend the "12:50 Club," Holy Redeemer's equivalent of detention, so named because it is held for an hour after school, until 12:50 p.m.

Most of the students had never been made to stay after school before, McCarthy said. "I had a counselor from Terrell come in and say to me, 'How do you get them to stay?' I just tell them to stay and there's no question in my mind -- they will stay."

"When I came to Holy Redeemer, I was thinking everyone was against me," said Terrell student Charlie Brown, 13. "But I found out the people at Holy Redeemer were there to help me. I learned to be more respectful to others and I therefore I came to respect myself."

Another one of the public school students, Ernest Byrd, 14, gave McCarthy a card that said, "I thank you for all the time you spent fussing at me and all you did for me and I mean it."

Andrew E. Jenkins, deputy superintendent of D.C. schools, said the city schools do not apply the same degree of discipline as parochial schools. But too much regimentation, he added, "is not necessarily desirable."