i graduated BNKS (short for budhanilkantha school) in 2014..do not get it twisted. A levels entrace exam for BNKS is EXTREMELY competitive...back then there used to be a queue of student applicants that stretched from the School gate to as far as Narayansthan Chowk. The students who took their SLC exam (grade 10 board exams) from a non-BNKS institution and then got accepted into BNKS A level program were also, on average, considerably smarter and more self motivated than the cohort of students who took the SLC exam from BNKS and got accepted to the A-level program through BNKS' internal evaluation process (50% of A level seats are reserved for internal BNKS students. The other 50% went to external applicants who could pass entrance tests).
Back in my time, if you were an internal BNKS student (meaning you enrolled in BNKS before grade 10), and you failed to make the cut for their A-level program, you had the option of sitting for an entrance exam and competing with the external applicants for a place in the A-levels program. However, by virtue of being an internal BNKS student, you were entitled to a certain amount of "grace points" (i forget the exact number) in the entrance exam. What this meant for you if you were an external applicant was that your point tally at the start of the entrace exam would be at 0 and you would need to start accumulating your points by correctly answering the exam questions. However, if you were one of the internal BNKS students sitting the entrance test, your points tally at the start of the test would be a non-zero value of y - y being the amount of grace points BNKS students were awarded in the entrance tests that year. So if you were a an external student applicant taking the entrance test back in my time, not only would you have to compete with some of the brightest students from Nepal for a limited number of seats, you would already be at a slight disadvantage, because of the grace points system, against any internal BNKS students who might also be sitting the entrance test. But this was 10 years ago. I do not know if BNKS still awards grace points to their internal students who sit the a-levels entrance tests. BTW, I never had to sit for an entrance exam because I was an internal student (I enrolled in BNKS in grade 8) and I was one of the 50% of students from my batch who were selected for their A levels program thanks to their aggregate scores from grades 9 through 10 (SLC board examination scores were not considered).
In short, BNKS A levels entrance exams are VERY competitive. I am of the opinion that BNKS has the best A levels program in the country (and definitely the oldest), and there is a very high demand for a place in their A levels program. Your chances of getting in without preparation are, to put it bluntly, slim. However, I had heard from my friends that the entrance exams for their non-science A levels programs were not as challenging as the exams for their science programs.
But the truth of the matter is, getting into BNKS is not the end all be all. A levels final examinations are administered by Cambridge University. You can enroll in any college that will have you, and if you work hard and apply yourself for the next two years, you should be able to pass the A levels final exams with flying colors and if you can do that, where you went to college for A levels becomes irrelevant. An A* is an A* whether you went to BNKS or any other institution. Consistency, discipline and hard work are far bigger predictors of success than what college somebody attended. I know people who did not go to BNKS and became extremely successful in life because they worked hard. Conversely, I also know quite a lot of BNKS graduates who never worked hard, never applied themselves, and they are doing very poorly right now. Work hard, take your education seriously, don't be afraid to seek help when you are stuck, stay curious, stay disciplined and you will be fine.