I have also been a teacher in one of high schools in Padang.
This is a common mistake made by Indonesians desperate to translate ‘salah satu‘ or maybe ‘sebuah‘.
In English, when we want to communicate one of many, we use the indefinite article ‘a/an‘:
This is sometimes called generic reference. The school in the example is not a particular school – we don’t yet know the name of the school, its address, etc. So far we’re just imagining a typical school. The image of the school in the writer’s mind will not be exactly the same as the image of the school in the reader’s mind, and that doesn’t matter.
I might use ‘one of‘ if I’m introducing more specific information about ‘a‘ school. For example:
Notice also that ‘one of‘ is followed by certain words, in particular:
For more examples, click here.
As a general rule – if you’re talking generally (generically!), use ‘a/an‘ for countable nouns. For uncountable nouns use ‘some‘.