When 13-year-old Andrew Savage heard the news about tragedy striking a Bay Area preschooler, he set out on a mission.

He would help 3-year-old Joseph Bialowas, whose leg was severed in August when his pregnant mother had grabbed him and jumped to her death in front of a commuter train in Santa Clara.

At home in Tiburon, Andrew and his parents felt shock and dismay at the little boy's fate. Andrew's heart went out to Joseph, who'd lost his mother and his leg in one horrific moment.

"It's a really traumatic thing for a person that age to go through," says Andrew, an eighth-grader at Brandeis Hillel Day School in San Rafael. "It's hard to believe it could happen."

Andrew created and distributed a flier seeking donations to a police officers' association trust fund for Joseph, who has no medical insurance and will need continuing medical care and therapy. Joseph, who was living with his mother at the time of the accident, now lives with his father.

Andrew's fund-raising efforts began to pay off immediately. As letters and donations poured in, he found himself writing hundreds of thank-you notes on Joseph's behalf.

Currently more than $7,500, the fund continues to grow. Andrew intends to stay involved "as long as Joseph needs me."

The child of a Catholic mother and Jewish father, Andrew attributes his spirit of tikkun olam (healing the world) to his Jewish education at Brandeis. "They teach us that when you do something good, it comes back to you," he says. He has learned that it's important to "try to do good mitzvahs."

While Andrew believes that "every person wants to do the right thing — all religions teach that," he adds — "I identify myself as Jewish, even though I was raised Catholic when I was younger…I have a lot of the beliefs that Jews have. I believe in doing good work for other people."

Andrew's outreach has not only prompted people to send financial contributions, but compelled some to also send heartfelt letters of praise.

A middle-school teacher wrote: "People like you make this world a better place. Even though I don't know you, I am proud of you."

A Tiburon woman wrote: "Thank God, we can read something beautiful about a young boy. Never change."

Still another: "What an incredible young man — Andrew Savage. I am 61 years old and becoming very disillusioned with society. This young man has done something to restore our faith. Thank you!"

Even children have been moved by Andrew's plea for help. Some have sent toys and comic books. In one package, Jennifer Bernstein enclosed a note explaining that her son Joshua, 3, "wanted to send [Joseph] some toys from his closet. Joshua carefully went through his room and decided what he wanted to give. We hope it helps."

At school, Andrew has urged students from all grades to help out. An eighth-grade bake sale brought in $70.

But Andrew's do-good spirit is not confined to helping Joseph. Andrew's mother, Barbara, said she was pleasantly surprised when he announced earlier this year that he would use his own money to sponsor a child in Guatemala.

Andrew and his sister, Sarah, a student at U.C. Berkeley, have also started the Children's Charity Group. To join, a child must be doing something charitable for another child. Their first new member is trying to raise funds for a friend who has leukemia.

In addition to his charitable work, schoolwork and helping with his father's software business, Andrew also enjoys hanging out with friends, playing soccer and learning martial arts. He hopes to add basketball and baseball into the mix, as well.

While Andrew remains casual and low-key about his goodwill efforts, his mother is more emotional. "Something else is happening here that is much bigger than anyone imagined," she says. "And it's reminding adults that they need to keep their hearts open."

Last month Andrew and his parents, bearing gifts in hand, finally had the opportunity to meet Joseph, who celebrated his fourth birthday in the Santa Clara City Council Chambers.

Andrew plans to stay involved in Joseph's life for quite a while. "He's going to need to have a prosthesis and have it replaced because he will keep growing," says Andrew. "He's also going to need therapy, and that costs a lot of money."