The 17-year-old girl, a senior at Gunn, was hit by a northbound train at the East Meadow Drive crossing shortly before 10 p.m. Tuesday, Caltrain spokeswoman Christine Dunn said.
Dunn said her death appeared to be intentional, but law enforcement officials have not confirmed it was a suicide.
On May 5, a 17-year-old boy, also a Gunn student, was struck and killed by a Caltrain at the same crossing. Messages from school officials indicated his death was a suicide.
Palo Alto Unified School District spokesman Scott Laurence said school officials learned of the girl's death around 6:30 a.m. today and quickly called in grief counselors for the students and staff.
"This is hard," he said.
Laurence said the teens may have known each other, but the deaths "are not believed to be linked in a critical way."
He said counselors today are speaking with the students in small groups and one-on-one, and will be available at the school as long as they are needed.
An event to help combat adolescent depression, "Breaking the Stigma: Adolescent Depression," will be held at 7 p.m. Thursday at Cubberley Auditorium at 4000 Middlefield Road in Palo Alto.
Another event of the same nature will be held June 18 at 7 p.m. at the Menlo Park City Council chambers at 701 Laurel St. in Menlo Park.
Various resources are available for Santa Clara County residents experiencing a crisis, including a 24-hour suicide hotline that offers counseling over the phone.
Many of the volunteers who staff the line have survived a loved one's suicide, said Gabby Olivarez, a senior mental health program specialist with the county and manager of the suicide prevention program.
The county also runs a suicide survivors' group where residents who have lost loved ones meet and support one another.
Olivarez said a basic mental health education can help parents and others recognize warning signs of suicidal behavior.
Those include disengaging from friends, family and social networks, losing interest in activities, and talk of suicidal thoughts. However, other signs can be less clear, she said.
Teens who are still developing a sense of self-awareness often don't recognize they have a problem, she said.
The service is staffed 24 hours a day. Residents in the north county can call (650) 494-8420, and residents in the south county can call (408) 683-2482.