Ruling on praying Jumu‘ah in the prayer room of the school, because the state does not give people a day off on Friday
Question

I am a Syrian citizen living in Turkey, working as a teacher in a Turkish school. It is well-known that the days off granted by the Turkish state are Saturday and Sunday. The time for Jumu‘ah prayer comes during working hours, so we gather the students and lead them in prayer in the prayer room in the school. Please note that the five daily prayers are not held in the prayer room, and the number of students is approximately five hundred. My question is: What is the ruling on praying Jumu‘ah in the school prayer room? If the prayer is valid, what is the ruling on reminding the students to be quiet during the khutbah?
Praise be to Allah.Firstly:
The basic principle is that there should not be more than one Jumu‘ah in the same town or city, except when there is an excuse such as it being a long way to the mosque, or the mosque in which Jumu‘ah prayer is held being too small to accommodate the number of worshippers.
It says in Kashshaaf al-Qinaa‘ (2/39): It is permissible to establish Jumu‘ah prayer in more than one place in a city or town, if there is a need for that, such as if the town’s mosque is too small to accommodate all the people; or if there is the fear of turmoil, meaning that there is some enmity among the people of the city, and there is the fear that trouble may result if they come together in one mosque; or the jaami‘ mosque is too far from some of the people in the city; or if the city is too big and the neighbourhoods are spread out and too far apart. In these cases, Jumu‘ah prayers offered earlier or later in different mosques are all valid, because Jumu‘ah prayers are offered in many places in big cities, without any scholar objecting to this, therefore there is consensus on the matter.
It is haraam to offer more than one Jumu‘ah or Eid prayer in a city or town if there is no need for that. It says in al-Mubdi‘: We do not know of any scholarly difference concerning that, except from ‘Ata’.
It is haraam for a ruler to give permission to an anyone to establish a second Jumu‘ah, when there is no need for that. The same applies to giving permission for Jumu‘ah to be established in more places than is needed.
If they establish Jumu‘ah in two places or more, when there is no need for that, then the Jumu‘ah prayer led by the ruler himself or the one to whom he has given permission is the one which is valid, because regarding the others as valid is like transgressing against the authority of the ruler or giving the people a reason to stop praying behind him.
If they are both the same in terms of having permission or otherwise – meaning that the ruler did not give permission for either of them – then the second Jumu‘ah is invalid, even if it is done in the biggest mosque. End quote.
If there is a mosque near you that is big enough to accommodate those among you for whom Jumu‘ah is obligatory, then it is not permissible for you to organize another Jumu‘ah prayer, and it is not permissible for you to stay away from Jumu‘ah prayer. Rather you should stop classes and go to the Jumu‘ah prayer, if that is possible and will not lead to a chaotic situation in the school.
If the mosque is not big enough, or it is so far away that it will be difficult to go there, then it is permissible for you to establish Jumu‘ah in the school or elsewhere, because it is not stipulated that Jumu‘ah prayer should be held in a jaami‘ mosque or a prayer room in which the five daily prayers are held. 
Secondly:
With regard to alerting the students and telling them to keep quiet during the khutbah, if this is done by the khateeb then there is nothing wrong with it, because it is permissible for him to speak to  the members of the congregation for a reason. Please see the answer to question no. 45651 .
If it is done by the teachers and organizers, then this is not permissible, because the one who attends Jumu‘ah is obliged to listen attentively to the imam whilst he is delivering the khutbah, and it is not permissible for him to speak to anyone else, even if it is asking him to keep quiet. The one who does that has engaged in idle speech, and there is no Jumu‘ah for the one who engages in idle speech. It was narrated from Abu Hurayrah (may Allah be pleased with him)  that the Prophet (blessings and peace of Allah be upon him) said: “If you say to your companion, ‘Listen attentively’ on a Friday, when the imam is delivering the khutbah, then you have engaged in idle speech.” Narrated by al-Bukhaari (892) and Muslim (851).
That applies if he tells them that by speaking; however, if it is done by means of a gesture, then it is permissible.
And Allah knows best.