This study aimed to build a benchmark testing to measure the linguistic competencies of post-basic students in government schools in the Sultanate of Oman. A simple random sample representative of the study population was selected, amounting to (542) male and female students, i.e. (15%) of the total study population, and to achieve the goal the study; The researcher used the descriptive analytical method by constructing a test based on the reference, consisting of (40) questions. After verifying its validity and reliability, the results of the study showed the following: 1. The diagnostic test used to measure the linguistic competencies of post-basic students in public schools in the Sultanate of Oman has high validity and reliability. 2. The percentage of students who are proficient in linguistic competencies exceeded the cut-off point set for the overall test of (37.5%), by a percentage of (52.03%), while the percentage of students who are not proficient was estimated at (47.97%), meaning that the students mastered the diagnostic test to measure linguistic competencies to a degree. Medium. 3. There are statistically significant differences at the significance level (α = 0.05) in the degree of linguistic competencies based on the benchmark testing diagnostic test due to the gender variable, and in favor of females. In light of the results of the study, the researcher recommended developing the skills of Arabic language teachers using modern teaching methods in teaching linguistic competencies, training them on how to prepare proficiency tests or mastery tests, reviewing educational policies related to writing Arabic language curricula, and benefiting from international linguistic tests of reference in assessing language competencies among students. School students in the Sultanate, preparing the classroom environment, making it a nurturing and attractive environment, providing modern technologies based on artificial intelligence in teaching the Arabic language curricula, and holding more specialized forums and seminars for Arabic language teachers. Keywords: benchmark testing, linguistic competencies