In 1950, Don Teodoro V. Santos, a prominent hacindero of Mabalacat, a philanthropist and a devout Roman Catholic, was approached by a group of civic-spirited people to build a school for the poor children of Mabalacat who found it hard to pursue their secondary education at Angeles City.

Without much ado, Don Teodoro V. Santos, realizing that he could be of much help to the people of Mabalacat, voluntarily donated the school site. He likewise chipped in a big amount of his money to start as his share of stocks for the school which was registered at the Securities and Exchange Commission (SEC) as MABALACAT INSTITUTE, INC. Together with his brother, Mr. Ernesto V. Santos, as majority stockholders, supported the school without expecting any dividends or financial gains, except to see the school operates progressively. Some concerned people of Mabalacat from all walks of life also contributed small share to start the corporation. Putting together all accumulated donations, Don Teodoro V. Santos began the construction of the main building along the McArthur Highway, Barangay Mamatitang, Mabalacat, Pampanga. Since the building was not yet finished, and yet classes were scheduled to start on June 1950, he found the house of Apung Lolong and Aling Lucing Garcia available to hold classes for the first and second year students. Thus, classes started in this house until the main two-storey building was completely constructed.

Mr. Irineo Mercado, the first school principal, together with his competent and mission-minded teachers, ably managed the school. The teachers started on a meager salary, and it ways supported by the founder. All through the personal support of Don Teodoro, the school managed to overcome all financial instabilities.

Down through the year, Don Teodoro V. Santos had become a consistent and generous benefactor of the school, especially during the year of 1959 to 1963 under the administration of the DOMINICAN SISTERS, Sor Amada Sahater and Sor Beatriz Alcober, O.P. During these years, the vision of Don Teodoro V. Santos to have well-rounded Christian education for the students started. Since then, the school began as a Catholic School, with Rev. Felipe Roque, Parish Priest providing the spiritual nourishment of the students.

On May 15, 1982, Don Teodoro V. Santos, with the help of his legal adviser, Atty. Richard V. Funk, reactivated and reorganized the Board of Directors in order to harmoniously work together with the school personnel for a more efficient management. The newly composed board unanimously elected Atty. Regalado P. Morales as General Manager and School Director to manage the school and exercised all the functions and responsibilities as provided for in the by-laws. During his term as General Manager and School Director, the inevitable increase in the school population served as an impetus to look forward and to reach out for better solution to growing problems. Through the joint venture of the school staff and faculty, PTAs and concerned citizens of Mabalacat, three additional classrooms were constructed. Aware of the vision of Don Teodoro V. Santos, Atty. Morales, a very religious man himself, continued the ideals of Don Teodoro of providing Christian education. He gave himself to this service, and even propagating our Christian Faith to the school staff and faculty members.

On September 14, 1983, Don Teodoro V. Santos died. As a fitting honor and to forever recognize his generous and philanthropic acts for the Institute, the Board of Directors unanimously passed a resolution renaming the school as DON TEODORO V. SANTOS INSTITUTE (FORMERLY: MABALACAT INSTITUTE) which was subsequently approved by the Department of Education, Culture and Sports.

Today, the Institute stands as among the progressive schools in the division of Pampanga for providing quality education, a consistent winner in academic contests and extracurricular activities.

It has a spacious and fully air-conditioned building where third year and fourth year students avail of the service of competent Instructors for all-year round high standard and up-to-date computer training.

At present, the school is managed by a set of Board of Directors who are imbued with the ideals and vision of the late Don Teodoro V. Santos, led by Atty. Richard V. Funk as President, Mr. Vicente D. Tuazon as Vice-President, and concurrently Principal, Mr. Roxan D. Morales as Treasurer, Ms. Consuelo C. Funk as Secretary and Judge Noli P. Quioc, Atty. Richard C. Funk, Ms. Corinne Funk-Zablan, Mrs. Amada F. Tuazon and Mrs. Dulce Morales as Members of the Board.