Chulalongkorn University Demonstration School was established on June 20, 1958, by Thanphuying Poonsapaya Navawongs na Ayudhya. The school was founded with the vision of creating an educational demonstration and a practical training center for students of the Faculty of Education, allowing them to gain essential teaching experience before graduating to become professional educators.

         In its early years, the school faced numerous challenges, particularly a lack of budget which resulted in the absence of a permanent campus. It was not until the tenure of Professor Ampai Sucharitakul as Principal that the school secured a permanent location. This site was originally the residence of a foreign faculty member teaching German at Chulalongkorn University—the home of Dr. Klein—located opposite what is now Triam Udom Suksa School.

       At that time, the building was in a state of disrepair. Thanphuying Poonsapaya Navawongs na Ayudhya, acting as Dean, successfully secured funding from the United States Operations Mission (USOM) to renovate the structure into classrooms. This became the first official building of the school. In 1997, Chulalongkorn University renovated this historic landmark to serve as the university’s official guest house, renamed “Baratha Raja Hall.”

         Initially, the school accepted students for Grade 1 and Grade 7 (equivalent to today's Grade 5). However, once the first cohort of Grade 1 students reached the secondary level, the school transitioned to admitting students exclusively at the Grade 1 level.

           Through the collective dedication of past principals, administrators, and faculty, the school has continuously advanced in academic excellence, personnel development, and facilities, earning the enduring trust of parents.

          Under the leadership of Professor Dr. Ubol Reangsuwan, the school underwent significant physical development. In 1964, the school received a government budget to construct modern, permanent facilities in Chula Soi 11, which serves as the current location of the Secondary School.

       CUD is recognized for its modern instructional systems and its unique, self-developed curriculum that extends beyond the standard requirements of the Ministry of Education. Our highly capable and dedicated personnel foster an environment of care and support. This close-knit relationship between teachers and students makes the school feel like a "Second Home," where students feel secure and supported in every aspect of their lives.

       By 1969, the student number had grown to over 3,000, ranging from Grade 1 to Grade 11. To manage this complexity and address the differing developmental needs of various age groups, the Faculty of Education divided the school into two levels:

• Primary School: Led by Professor Dr. Ubol Reangsuwan.
• Secondary School: Led by Professor Dr. Wichit Srisa-an.

The title of the head administrator for the Secondary School has evolved over the years:

• 1975–1976: Under Dean Assistant Professor Dr. Pinyo Satorn, the Dean of the Faculty of Education concurrently held the title of "Director" by position.
• 1976–1980: Under Dean Professor Ampai Sucharitakul, the University Council appointed the Principal to serve as "Associate Dean and Acting Principal."
• 1997: Following administrative reforms, a new regulatory framework established the title "Associate Dean and Director." The school's official designation was also updated to "Chulalongkorn University Demonstration Secondary School."