For a man to work as a teacher in a high school for girls, where he meets them with no barrier and most of them may adorn themselves and show their charms – as is the case in the country where the questioner lives – no wise man would doubt that this is haraam, because of the bad effects and evil results for both men and women. We have discussed these evil results in the answer to question no. 50398.
It says in Fataawa al-Lajnah al-Daa’imah (12/149): It is not permissible for a man to teach girls directly because of the serious dangers and grave consequences involved in that.
It also says (12/156):
Firstly: Mixing between men and women in schools and elsewhere is a great evil which may corrupt religious commitment and worldly interests. It is not permissible for a woman to teach or work in a place where men and women mix, and it is not permissible for her guardian to give her permission to do that.
Secondly: it is not permissible for a man to teach a woman who is not wearing hijab, and it is not permissible for him to teach her when he is alone with her, even if she is wearing proper hijab. When a woman is with a man who is a non-mahram her entire being is ‘awrah. As for covering the head and showing the face, this is not full hijab.
Thirdly: there is nothing wrong with a man teaching a woman from behind a screen in women-only schools, where there is no mixing between male and female students, or between the (male) teacher and (female) students.
If they need to ask him questions, it should be means of closed circuit TV, which is well known and easily available, or via the phone, but the students should beware of speaking softly. End quote.
With regard to what you have earned from this work, there is nothing wrong with your benefiting from it, because this salary that you have earned is in return for giving lessons (which is basically permissible work), and the prohibition is because of the mixing, as stated above.
But you should hasten to leave this job and look for another job which is free of the risk of doing something haraam and falling into fitnah.
We ask Allaah to guide us and you.
And Allaah knows best.