Translation:Children go to junior high school when they are thirteen years old.
Hmmm. This example shows that the general rules are (not surprisingly) just a simplification.
"chodzą" could potentially work, but that would mean that generally children aged 13 attend junior high school.
"idą" means that they "go to" = "start" junior high school when they are 13.
I see that this sentence has translation ENG->POL blocked... good call, I guess.
Ah, thank you! I guess I got confused - as in Germany a "Gymnasium" is actually very similar (except the starting age and some other details) to a "gimnazjum". So I missed the incongruence with the English. It seems like a true false friend, at least for me :) but still, I am wondering why it was accepted earlier?