A vision of having built a secondary school in Alapan might have been the idea of the late Brgy. Capt. Emiliano "Miling" T. Barzaga. It was decided that the high school building be established just within the compound of the elementary school (the small parcel of land)
Through the help of Mayor Emmanuel "Manny" Maliksi the two story building was established August 29, 2010 of with four initial classrooms and named Imus National High School-Alapan Annex. On its first year of existence with initial enrollment of 150 students in all year level with five teachers who with sincere intentions and precedence to help and provide students and allowed themselves to be assigned in Alapan namely; Yasmin F. Santiaguel (Filipino & Social Studies), Marilou P. Merino (English), Daniel de Vera (Mathematics), Edgar A. Rivera (Science and Technology) and Jonathan S. Jimenez (MAPEH. TLE and Teacher-in-charge).
The first elected Parent Teachers Association (PTA) President Mrs. Jessel P. Parani with other officers plays an important role in the development of education to continually support the newly established school in Alapan Annex who devoted their time and exerted effort to convince the community.
On April 1, 2011 the first sets of graduates finished their high school in a simple but meaningful way which was succeeded by the parents, teachers, town officials, and other guests.
On June 2011, the school's permanent fence was built through the effort of ever supportive and dedicated Brgy. Captain Anastacio "Tanny" T. Barzaga. He continued the dream of his father to continue to help the community members of Alapan II-A. The fund for the construction of fence was through the help of the present Mayor Homer T. Saquilayan.
July at the same year school canteen was also establish to continue service to the students.
On May 2013, 14 new national funded teachers and one locally funded utility. Headed by Mrs. Maria Luisa F. Candelaria Head Teacher III/OIC, INHS-Alapan Annex. The GPTA President is Mrs. Jessel P. Parani and SGC President is Mr. Ricardo Pangilinan.
At present INHS-Alapan Annex had an additional 7 nationally funded CSU headed by Ms. Cynthia T. Abeledo Head Teacher VI-Filipino Department from INHS-Main.
With the new PTA President Mr. Dick Facundo and SGC President