The curriculum was varied and specialized, following a trimester system, and students were encouraged to address their teachers by their first names and focus on independent learning.

[citation needed] Alongside traditional disciplinary staples such as English, mathematics, science (chemistry, physics, and biology), physical education, and social science (divided evenly between history and geography), Thornlea also offers courses in the fine arts, music (vocal, choral, orchestral, wind ensemble and jazz), drama, Introduction to business studies (General, marketing, and accounting), and design and technology (automotive maintenance, communications, media & film studies, woodworking and engineering, cosmetology).

A survey course in philosophy that is generally popular among Thornlea seniors has also been offered inconsistently over the years, depending upon the availability of a qualified instructor.

A variety of creative writing courses have also been offered over the years, again, the existence of which has typically been a function of instructor interest and availability.

At some point the experiment was abandoned, and a new southern wing was built during the 2000–01 school year, complete with windows for every classroom that has an externally facing wall.

[3] The ACAM program (Academy of Creativity and Multimedia) serves to provide all students wishing to pursue a career in the arts a specialized course.

Various courses can be taken under the AP Program, including Art, Advanced Functions, Biology, Chemistry, Physics, Calculus and French.

[5] SHSM (Specialist High School Majors) is a program which enables students to develop relevant skills for various industries.

Thornlea students often assist in the social activist life of Thornhill, and have, in the past, helped organize the Terry Fox Run, as well as the Walk Against Male Violence.

Most recently, in the 2023–2024 school year, the TN Magazine was handed over to a new editor-inchief, who, alongside two executives, decided to rebrand it back to Deadline.

This club is responsible for the wiring and behind the scenes of various assemblies and events throughout the year, including drama plays and the TWIC Wellness Fair.

The Tech team uses soundboards, lightboards, cameras, speakers, wiring and various other forms of equipment to ensure that these events run smoothly.

These teams include soccer, tennis, rugby, basketball, cross country, volleyball, golf, swimming, rock climbing, curling, skiing, snowboarding, badminton, track and field, ultimate frisbee, flag football and baseball.