日本では、その年の4月1日時点で満6歳に達している児童が小学校に入学します。 I'm wondering why 達している? I've learned it acts like Present Continuous, but Google gives me Present Perfect. Why not plain suru or shita?
It’s because they’re saying the children must be fully 6 years old. It is were する, then it would sound a bit off and feel like they’re saying the children “will be six years old”. If it were した then it would sound like you’re saying the children “had been six years old”. As it’s currently put 達している they’re implicitly saying the children are currently a full six years old.
達する is much like various other verbs: くる, 結婚する, etc in that these verbs are instantaneous: they’ve happened or they haven’t happened yet. There’s no instant between not being fully six years old and being fully six years old. Once you’ve hit the mark, so to speak, what you’re describing as the continuative is really more like the present perfecting.
So, for example,
doesn’t mean “i’m getting married [right now]”. Instead it means you’re already married (perhaps you’ve been now been married for 20 years).
doesn’t mean “I’m on my way going to Tokyo”, it means “I’m in Tokyo”.