Questions & Answers about Za tydzień zaczyna się rok szkolny.
How is the adjective szkolny formed from the noun szkoła?
It uses the suffix -ny, which is one of the standard endings for creating relational adjectives. Notice the consonant change: the hard ł in szkoła softens to l before the suffix, giving us szkolny instead of "szkołny".
Why is the adjective placed after the noun (rok szkolny) instead of before it?
In Polish, classifying or relational adjectives normally go after the noun. Because szkolny tells us exactly what category or type of year it is (an academic one) rather than describing an opinion or physical trait (like in dobry rok), it strictly follows the noun.
Why do we use the reflexive zaczyna się here instead of just zaczyna?
The non-reflexive zaczynać requires a direct object, meaning somebody starts something (e.g., the teacher starts the lesson). Because the school year is just starting on its own and isn't starting something else, we have to use the reflexive zaczyna się.
Why does the sentence use za tydzień to say "in a week"?
To express that an event will happen "in" a certain amount of time from now, Polish uses the preposition za followed by the time period in the accusative case. Using "w" here is a common trap for English speakers.