This is the 15747th most frequent Polish word.
szkolnymi
"Szkolnymi" means "school-related" or "pertaining to schools" in English.
Here, 'szkolnymi' modifies 'przyborami,' indicating that the supplies are related to school.
Dzieci bawiły się szkolnymi przyborami.
The children were playing with school supplies.
In this context, 'szkolnymi' describes 'korytarzach,' specifying that these are school corridors.
Chodziliśmy po szkolnymi korytarzach.
We were walking through the school corridors.
The word 'szkolnymi' is used to characterize 'projektami,' showing they pertain to school.