Ruling on teaching in a Christian school
Question

                Is it ok to teach at a catholic school?.
Praise be to Allah.The shar’i ruling differs 
    depending on the state of the school referred to in the question. 
1.
If it is a religious 
    school, in the sense that it was established to produce priests, monks and 
    nuns, and it is working to establish a new generation of this class of 
    people, then we do not think that you should work there, and we can only 
    advise you to be cautious and to keep away from it, even if you are being 
    called to teach other, secular subjects, because by taking part in working 
    with them you will become part of their institution, and it is as if you are 
    helping them in their kufr which they want to teach to the children. 
2.
But if it is an ordinary 
    government school, but has a Christian administration that wants to teach 
    the Bible, and it is limited to that, then in that case there is nothing 
    wrong with you working there and becoming part of the faculty, so long as 
    you adhere to the commands of Allaah and observe proper Islamic hijab, and 
    perform all acts of worship on time, and have a good attitude and treat 
    others well, and avoid forbidden things, one of the most serious of which is 
    loving the kuffaar, feeling comfortable with them and imitating them.  
When working with them, you 
    should be keen to spread the truth and call people to it, and rid whoever 
    you can of the darkness of ignorance and shirk. But if the school requires 
    you to do any Christian acts of worship or traditions, or it is mixed (men 
    and women together), or you fear that you may be dazzled by specious 
    arguments as the result of mixing with the Christians, then in that case it 
    is not permissible for you to work there, and you should not continue to do 
    so, rather you must leave and shun it for the sake of your religious 
    commitment and so as to protect yourself from falling into the traps that 
    the shaytaan sets for the sons of Adam. 
Allaah says (interpretation 
    of the meaning): 
“O you who believe! 
    Follow not the footsteps of Shaytaan (Satan). And whosoever follows the 
    footsteps of Shaytaan (Satan), then, verily, he commands Al‑Fahsha’ [i.e. to 
    commit indecency (illegal sexual intercourse)], and Al‑Munkar [disbelief and 
    polytheism (i.e. to do evil and wicked deeds; and to speak or to do what is 
    forbidden in Islam)]. And had it not been for the Grace of Allaah and His 
    Mercy on you, not one of you would ever have been pure from sins. But Allaah 
    purifies (guides to Islam) whom He wills, and Allaah is All‑Hearer, 
    All‑Knower”
[al-Noor 24:21]
We should not forget to 
    point out here the danger of these schools when they are opened in Muslim 
    countries; in that case they are a tool of colonization by stealth, and an 
    obvious means of corruption, concerning which many fatwas have been issued 
    by scholars and academic institutions from the time when they were first 
    established. 
And Allaah knows best.