Welcome to Tustin Adult School & Sycamore High School. Tustin Adult School offers classes for adults and concurrent students to earn a high school diploma, as well as for adults to learn English as a Second Language (ESL). Sycamore High School is an independent study school where students do their learning outside of the school setting and meet with a credentialed teacher once a week for testing and additional assignments. Contact our office staff to learn more about these programs. Call 714-730-7395.