Lagao National High School was established as an annex school of General Santos City High School in 1988. This was a joint project of Schools Division Superintendent Lucrecia M. de Leon, and the Office of the Congressman Albert W. Antonio.

Mrs. Esther T. Ladera was designated as Principal-In-Charge of the Annex during 1988-1989 when they are 23 teachers hired and 692 enrollees that time. In 1989, Mrs. Ladera, by virtue of her promotion as principal of Pedro Acharon Elementary School, transferred the second batch of first year enrollees to Pedro Acharon Elementary School and with the approval of the School’s Division Superintendent, move the second year students to Dadiangas East Elementary School. Mr. Bonifacio Ferrer was designated as Principal-In-Charge, with the assistance of Mrs. Virginia C. Rebucan.

In 1990, Dr. Constancia Q. Hintay, Schools Division Superintendent appointed Veronica C. Punzala, as Officer In-Charge of the annex school. the growth enrollment and the lack of classrooms demanded for more flexible management that classes had to be divided into two shifts. The first year attended the morning shift while the third year followed the afternoon schedule, with classes ending at 8:00 o’clock in the evening. Meanwhile, the second year classes remained at Dadianges East where Mr. Ferrer provided more rooms to accommodate the increase in enrollment.

In mid 1990, DECS and Congressman Antonio caused the purchase of two-hectare land worth P2.4M from Mr. Sofronio G. Manansala at Purok Malakas, Brgy. San Isidro. Preparation for the transfer of annex school to the site went on in earnest. Finally, May 11, 1991 the ground breaking of ceremony took place of the site. June 1991, the annex school transferred to the site. Mrs. C. Rebucan was designated Teacher in-Charge. DECS at that time has a new Schools Division Superintendent in the person of Dr. Constancia Q. Hintay.

Under the dynamic leadership of SDS Hintay, parents. Parents Teachers Community Association (PTCA) Officers and community, officials were mobilized to provide the school with classrooms and other facilities. Parents and stakeholders wholeheartedly supported the school. The lumber was solicited from coco plantation owners through the efforts of SDS Hintay. Donation of lumber came from the Department of Environment and Natural Resources. While Bayanihan Sawmill sawed such lumber for free. Consequently, 20 nipa makeshift classrooms were put up. Classes went on in these classrooms with only the nipa root secured both the students and teachers from any form of elements.

The parents, PTCA Officers, teachers, DECS, local government and barangay offcials worked together to provide the school with free resources needed to make the school environment more conducive to learning. And soon enough, these selfless efforts made way for the hiring of additional new teachers and in April 2, 1992, the school conducted its first Commencement Exercises with 292 students. The graduation stage was provided by Mr. Carlos Yusepeng and Mr. Lob of Taiwan who augmented the contribution of the parents of the graduating students.

Finally, in 1993, Lagao National High School became independent from its Mother School. Mrs. Virginia C. Rebucan was designated Teacher in-Charge. The annex at Dadiangas East Central Elementary School was retained under the management of its Teacher-in-charge, Mrs. Rafaelina Hitalia. Later, the Annex became Irineo Santiago National High School of Metro Dadiangas.

It was also in 1993, Lagao National High School answered the clamor of the officials of Brgy. Mabuhay for a high school and opened an extension school at Brgy. Mabuhay under the leadership of Mrs. Francisco M. Espinosa. In 1995, the extension school obtained its dependence and was named Engracia L. Valdomar National High School. Meanwhile, in 1995, Mrs. Rebucan became the full-fledged principal of LNHS. She provided the leadership to 122 teachers and staff over 3,000 students then. Three years after its dependence from its Mother School, LNHS became a performing school in the Division of General Santos City.

In 1999, the growth in enrollment at the main campus could hardly be contained due to influx of enrollment that another annex school had to be opened in Barangay City Heights, due to the need to establish a secondary school in Barangay San Isidro, tis new annex was transferred to Barangay San Isidro.

Aside from the Basic Education Curriculum, the school created special programs to address specific learning needs. The Evening Class Special Program was opened in 2001 while the Special Education Program was established in 2009. The Special Science Class was created in 2010.

Mrs. Virginia C. Rebucan was able to lead the school as school principal for 21 fruitful and successful years. She retired on September 30, 2012.

After the retirement of Mrs. Rebucan, Mr. Mario M. Bermudez, the Officer In-Charge Assistant Schools Division Superintendent of General Santos City served as the concurrent principal of LNHS for 3 months.

Then, in January 2013, Mr. Efren B. Lemana was designated as the School Head of Lagao National High School. It was during his time that Special Program for the Arts, Special Program in Journalism, Special Program in Sports and Open High School Program were conceived.

In 2015, Mr. Angelito C. Llanos was assigned as the School Head of LNHS. During his term, the Special Science Class, now known as ESEP or Enhanced Science Education Program, gained its regional recognition. With the promotion of Mr. Llanos as District Supervisor in 2016, he was replaced by Mr. Rustico S. Pelonio, Jr.

Lagao National High School is now an institution to reckon with. the achievements and recognitions of its teachers and students in different disciplines from the division level to the national level manifest the holistic and integral development of each of the members in Lagao National High School community.