This is the 2207th most frequent Russian word.
гражданами
"Citizens."
Here, 'гражданами' refers to individuals recognized as members of the country and incorporates the instrumental case indicating the role or category they fall into.
Все гражданами страны должны следовать её законам.
All citizens of the country must follow its laws.
In this sentence, 'гражданами' denotes the residents or inhabitants of the cities, again in the instrumental case, used to describe the entities filling the cities.
Города наполняются гражданами в выходные дни.
Cities are filled with citizens on weekends.
'Гражданами' in this context means the general public or individuals as residents of the country, utilizing the instrumental case to indicate the persons schools interact with.