This is mainly because you're in primary school, so schools repeatedly do this because many kids are young and will "panic, cry, and run everywhere" when a situation like this happens. So, primary / elementary schools do this all the time, until they know what do to. In schools with higher grade levels, they don't do this a lot, as kids are older, and know what to do, and won't cry, panic, and run all over the campus. Elementary schools / Primary do this because kids there are 5 - 12. It may seem annoying to you, I strongly bet $5 that if a fire happened, and your school barely did fire drills, you, and everyone at your school will be screaming, running home, and panicking. Anyways, my schools: Elementary / Primary: About 1 per 3 weeks Middle School: Only do this in the beginning of the year, about 3 times.
My high school has the testing once every 2 years. Its actually their way for getting the whole school together to give detentions and shiz. I got 1 detention just by walking through the matric corridor because of the fire alarm......... ... ... *sighs*