Praise be to Allah.
If the situation is as you describe, then you must leave this school and beware of its evil, and keep away from it and its people, in order to protect your religious commitment, belief and morals from these evildoers among the students, male and female, and this bad society. You must do your utmost to move to a safe school or a safe city or a farm or whatever is farthest removed from danger to your religious commitment and morals. This is what you must do, even if your father does not approve, because the Prophet (peace and blessings of Allaah be upon him) said, “Obedience is only with regard to that which is right and proper.” And he (peace and blessings of Allaah be upon him) also said, “There is no obedience to any created being if it involves disobedience towards the Creator.” Sitting among evildoers, people of shirk and those who do not pray, and sitting among girls who make a wanton display of their beauty and are unveiled poses a serious danger to one's beliefs and morals, so it is not permissible for the Muslim to remain in this situation. Rather he must beware of this society and move away from it to a society that is better and safer for his religious commitment even if he has to travel from one city to another, such as going to Makkah or Madeenah in order to study in al-Masjid al-Haraam or al-Masjid al-Nabawi, because there are teachers there who are people of knowledge, virtue and sound ‘aqeedah, whether his parents approve or not, because obedience to parents is only with regard to that which is right and proper, not in matters of sin and disobedience, as stated above. And Allaah is the One Whose help we seek.