Admission is based on STS High School Placement Test scores, grades, recommendations, and personal interviews.

The school population is 78% Catholic; student ethnic distribution is 42% Hispanic/Latino, 26% White/Other, 20% Multiracial, 6% Asian, 4% Filipino, and 2% African American.

[5] In July 2013, it was revealed that St. Lucy's had terminated the employment of a teacher who had married a partner of the same sex, following changes to California's marriage law.

Ken Bencomo had taught at the school for 17 years, but had his contract terminated by Assistant Principal Sister Helen Dziuk after a photograph of the marriage appeared in a local newspaper.

"[6] A public petition was launched by alumnae and the St. Lucy's community calling for Bencomo's reinstatement, which proved unsuccessful.