Quality is the ultimate goal of any educational institution. It spells out success and failure of an organization and its attainment connotes excellence in performance which is the very vision of every educational institution. The quality of education is always manifested in the student's level. As such, it becomes imperative for every educational institution to exert the best efforts in order to attain the quality it aims to pursue. At present, there are problems in schools as to the students' academic performance. Such is a scenario not only in the public schools but also in private schools in terms of basic education. This study aimed at investigating the academic performance in the NAT VIS.Y 2014-2015 which involve the least-mastered skills and the factors that affect the low academic performance in the NAT VI. This study used documentary analysis of NAT results from the Bureau of Assessment (BEA)formerly National Education: Testing and Research Center (NETRC) to identify the least mastered skills of the five academic subjects such as English, Math, Science, Filipino and HEKASI. It also used descriptive method which focused on the different factors that affect the low academic performance in the NAT VI in terms of teacher's competence, parental support and pupil's attitude. The study involved 1 Master Teacher to assess the teaching competence of 28 Grade Six teachers and these 28 Grade Six teachers to assess the parental support and pupil's attitude of Camarin D Elementary School It utilized a survey questionnaire to gather the data from the respondents. The findings of this study revealed that the least mastered skill in English is "Identify supporting details to justify a conclusion". In Math, "Identify congruent polygons", In Science, Identify the characteristic of the earth's interior layer with PCR of. In Filipino "Nagagamit ang panipi at kuwit sa tuwirang sinabi ng tao" In Hekasi, "Ang teritoryo ng Pilipinas at mga Likas na Yaman Nito-Napahahalagahan ang mga hangganan at ang matalinong pagpapasya sa paggamit at pangangalaga ng likas na yaman". This study also found that the factors affecting the low academic performance in the NAT VI are teachers' competence, parental support and pupils attitude. The teachers are equipped with knowledge, skills and attitude. "Sometimes" pupils have parental support Some parents do not have enough time to help their children in their study that result to poor academic performance of their children,Since findings revealed that the reasons why pupils got low in the academic performance in National Achievement Test (NAT) are they don't have enough parental support that resulted to some negative attitudes toward study and some teachers' high standard of teaching failed to reach the student level, therefore the intervention program focused on the improvement of pupils attitude, parental support and teacher's competence. Based on the findings and conclusions of this study, the following are recommended: provide additional instructional assistance to teachers on content re-orientation of least mastered skills on subject they are teaching: strengthen training programs that would enhance the teachers' competence; encourage parents to support and monitor their childrens academic performance; pupils should attend classes regularly and develop good study habits. The teacher should find ways to communicate with parents to encourage them to support their children. If the parents can't come to school, the teachers should conduct home visitations. The parents should be involved in their children's preparation for the NAT. The pupils should develop positive attitude toward study through the help of their parents and teachers. They should always seek assistance from their teacher when it comes to a subject that can hardly cope with. Consider the Intervention Program developed by the researcher to improve the academic performance of pupils in the NAT VI.