Meredith Grcina was scared and overwhelmed when she enrolled in Clayton Valley High School in Concord as a freshman. She missed the closeness of the 30 students in her eighth-grade class at a small Christian school.

Feeling alone in a sea of 2,000 students, she considered transferring to a smaller private high school. But then she made a couple of good friends in her classes and got swept up in school events, such as dances and football games. Now she is happy at the school.

Meredith, a 15-year-old sophomore, says what made a difference for her was Clayton Valley's new "smaller learning communities," clusters of students who have the same teachers.

"It feels like a little community," she said. "I think it helped a lot. I think it's a really good way to introduce freshmen to high school."

Aiming to prevent students such as Meredith from getting lost in the crowd, Clayton Valley and the five other large, comprehensive high schools in the Mt. Diablo school district are following a national trend to break up their campuses into smaller groups of students and teachers.

Backed by a $2.2 million federal grant, the six high schools are in their second year of trying to transform their campuses from impersonal, sprawling institutions into places where students feel more at home.

Millions of dollars from private foundations and the federal government are invested in the theory that students who feel less isolated will have higher grades and fewer behavior problems and prevent school violence. The federal grant program was created after the deadly shooting at Columbine High School in 1999.

Although few students or teachers disagree with the goal, reorganizing the Mt. Diablo high schools from top to bottom has been tricky. Student scheduling is a headache. Some teachers are reluctant to change their ways. And some students feel limited in the classes they can take and the other students they can get to know.

The way it works is each student and teacher is assigned to a community, also called a house, cluster, academy or pathway. Teachers in core classes such as English, math, science and history share the same students, so they can work together on cross-curricular projects and track students more easily.

Pat Tillery, a Clayton Valley High sophomore, is one of the skeptics.

He doesn't like the idea that he can't pick teachers from a different community. For example, the best English teachers may be in one community and the best math teachers in another. He also thinks it is harder to meet more students if the same ones are in many of his classes.

"I like being in a bigger environment, because I like not as much attention on me," he said. "I like being lost in that crowd."

Clayton Valley Principal John Neary acknowledges that a limited selection of teachers is a drawback to breaking up the school into communities. But, he said, the traditional structure of large high schools was not working for many students.

"That was my big sales pitch when I first started," he said. "What are you afraid to change from? What are you so proud of that you are afraid to try something else? Not much."

Clayton Valley is farthest along in process, having assigned every student and teacher in the school to a community. College Park, Concord, Northgate and Ygnacio Valley high schools have clustered the ninth- and tenth-graders, and Mt. Diablo High has done it just in ninth grade.

The schools all are developing academies or pathways that focus instruction on a career. Clayton Valley, for example, has five interest pathways: public and human services, health and environment, engineering and technology, international business and marketing, and the arts and multimedia.

But some students are still unclear on how the whole system will work. A student editorial in a paper published by Clayton Valley's beginning journalism class described the confusion:

"For the most part, the change in our school has not been very effective. Most people can't see the difference. Some people don't know which pathway they are in, and some don't even know what (smaller learning communities) are."

Supporters of the change said it is too early to judge its effectiveness, but they already have seen some positive results.

Sarah Lovick, a 1996 graduate of Clayton Valley and now an English teacher who heads the public and human services pathway, said students are starting to get to know one another better.

"I see them in class giving kids more of a chance, kids who might have been an outcast for a number of reasons," she said.

A district survey of students in all six high schools in the fall of 2002 found that students who were part of a smaller learning community had a more positive outlook and felt more connected to their school than those who were not.

Many researchers agree that smaller schools are better than larger schools at preventing dropouts, raising test scores and improving behavior and attendance. Stuck with large high school buildings and no money to build or operate smaller ones, many schools around the country are trying to capture the benefits of the smaller schools on larger campuses.

"In the field of high school reform, where there are few good ideas, it's one of the few good ideas floating around," said Michael Kirst, a Stanford University education professor and the co-director of Policy Analysis for California Education, a joint Stanford-UC Berkeley research group.

One key to success seems to be autonomy. A smaller learning community has to be given the freedom to build its own identity and agenda and make decisions separate from the larger school, according to research review by the Northwest Regional Educational Laboratory, which is providing technical support to the federal grant recipients.

Support from teachers and the community is also important, said Joan Shaughnessy, who directs the lab's smaller learning communities project.

"It's not easy to do," she said. "It's very hard to change the culture of a school, which is what you are trying to do."

Each community at College Park has its own building and its own name: Lassen, Whitney and Shasta.

The move was hard for some teachers who wanted to stay near other teachers in their departments, said Judy Young, a math teacher and coordinator of the communities. It was challenging to break out of their comfortable social groups to work with teachers in other departments, she said.

This is Young's first year in a classroom outside the math department in her 24 years at College Park. She still hasn't totally unpacked.

"It's easier for me to stay and do things the same old way, but maybe that's why we are doing it," she said.

The biggest headache has been scheduling. Teachers expected to be able to assign cross-curricular projects. But scheduling glitches caused a few students to be assigned to each class from outside the community, making common projects impossible.

Still, English teacher Andrew Nolan said he has collaborated more with other teachers than in the past. They often meet to discuss students and plan. When there is a problem, teachers meet together with the parents.

For example, after Nolan overheard a girl say something rotten about another teacher, the two teachers met with the girl and her mother. Nolan learned more about her situation, and they came to an agreement that has improved her attitude vastly and her work moderately.

"It's much easier to become more invested in a kid," he said.

Lists of kids who received at least one F on their quarterly report cards were distributed to teachers for the first time this school year. Teachers could more easily see if students were having trouble in many classes or just their own.

"It's a way to let the kids know that people care about them," Jessie Andresen, a consultant hired with the grant money to do counseling and ease the transition to College Park.

"Teachers are aware of more than maybe they think they are."

Andresen also has started an after-school workshop called "Life Issues for Teenagers" as an alternative to suspension or detention.

In an ideal world, the district would build more, physically smaller schools, but it must deal with reality, Nolan said.

"I don't believe anything you do at a school this big is going to solve it," he said. "But does it make it better? I believe so."