There was a time when a city's high school was the center of town, the social hub and a thread of commonality linking students past and present.

Residents came out in droves to support the football and other teams, and students were more aware of events in their community.

It was a give and take relationship.

We support you, you support us. We come to your games, we donate to your booster program and in return students had more respect for the city, its properties, their classmates and neighbors.

Now, many cities in Contra Costa and other counties have grown so large that they boast two, sometimes three high schools, some with 3,500 kids or more. Many high-school students feel disconnected from their community, and the community in return has detached itself from them.

Barbara Holland, director of the National Service-Learning Clearinghouse in Scottsdale, said a gap has formed between students and their communities.

In recent years several schools have started to re-establish the connection by adopting community service programs, which are developing into service-learning curriculums.

Service-learning combines community service and volunteerism with learning objectives.

"Schools and education have become distanced from community life and issues," Holland said. "With service-learning, not all the learning occurs within the walls of the classroom. It takes learning into the community."

For example, instead of a biology class remaining in the classroom to discuss water pollution, a service-learning curriculum would take students on a field trip to a local creek. The class would clean up the area. While removing trash and debris, students could take samples of the water and soil to test back in their classroom.

Students would be able to see a water system and the polluting factors it faces in action, first-hand, and the community would reap the benefits of their hard work.

That's work that seniors in the Liberty Union High School District in Brentwood have become very familiar with. All seniors are required to complete 20 hours of community service with a nonprofit organization to graduate.

The district has had a community service program for 10 years, but it's only been a graduation requirement since 2002. The program is called Teens Link with Community, or TLC.

Marty Aguilera, community service coordinator, said students often go above and beyond the 20-hour requirement.

"Some kids don't realize how much they're going to get out of it," Aguilera said. "They're reluctant to do their 20 hours and then they feel really good about it and enjoyed what they did so they keep going."

Aguilera said the district's program is service-learning because it's tied to the students' American government class, teaching them about participatory democracy.

Holland said service-learning encourages students to think of themselves as active members of their community.

"Part of the idea is that teachers and schools are very enthusiastic about standards and the degree of learning, but also that we're building and developing socially responsible students," Holland said.