Benefit of doubt dear . Shari'ah is absolutely silent over the issue and there is no injunction in sources of shari'ah (Quran and Hadith) which explicitly or implicitly (indirectly) proscribes or forbids co-education (Allah maaf kare if I am wrong but I have not been able to find any scholar providing authentic reference from Quran and Hadith which exclusively bars co-education or impels absolute gender segregation no matter what). Islam is very very strict in observation of modesty and Allah (SWT) absolutely abhors fornication and adultery, there is no second opinion about it; but that is a different case, there are ways prescribed in Islam on how to deal with those who conduct immodest act. Most of the modern muslim scholars use the pretext of modesty and analogy of western societies to logically justify their harsh stance against co-education and ordinary gender commixing. During the times of Prophet (SAW) masjid served the purpose of both place of worship and education. Prophet (SAW) himself allowed women to come to masjid even when men were present so this implies that co-education should not be considered absolutely haram in shari'ah; however even Prophet (SAW) were very cautious in observation of ethics and morals to avoid fitna. What kind of fitna Holy Prophet (SAW) envisioned has not been clearly emphasized by the scholars, nevertheless fitna could have been of two logical types, 1. spread of immodesty and 2. medieval arab culture where a mere suspicion over female relative could trigger tribal warfare. Anyways, almost all the religious scholars set their focus on spread of immodesty fitna alone and recently scholars are presenting the scenario of western society as a logical justification against co-education. Schools are relatively modern system of institutionalized education; conditions of Pakistani institutions where predominant number of schools and colleges are single sex exhibit high level of violence, gangs and political activities in boys only institutions of low level education which then continues in universities; not to mention harassment and sodomy which is even noticeable in religious schools (madrassahs), that is a more severe immodesty in Islam. We can blame bad governance and management but issues are of purely social and cultural base like on one hand we see highly unsocial and untoward conduct and attitude of males towards females in our society not only in public places but at homes as well, but on the other hand we see sharp rise in level of secret relationships, number of brothels and women related violence for which we usually blame cell phones and communication technology but not our mindsets which have developed in highly segregated environment . I think the time has come for a debate on pros and cons of every aspect instead of finding religious excuses for cultural connotations. Allah (SWT) has mentioned in the Quran:

يَا أَيُّهَا الَّذِينَ آمَنُوا لَا يَحِلُّ لَكُمْ أَن تَرِثُوا النِّسَاءَ كَرْهًا ۖ وَلَا تَعْضُلُوهُنَّ لِتَذْهَبُوا بِبَعْضِ مَا آتَيْتُمُوهُنَّ إِلَّا أَن يَأْتِينَ بِفَاحِشَةٍ مُّبَيِّنَةٍ ۚ وَعَاشِرُوهُنَّ بِالْمَعْرُوفِ ۚ فَإِن كَرِهْتُمُوهُنَّ فَعَسَىٰ أَن تَكْرَهُوا شَيْئًا وَيَجْعَلَ اللَّهُ فِيهِ خَيْرًا كَثِيرًا
مومنو! تم کو جائز نہیں کہ زبردستی عورتوں کے وارث بن جاؤ۔ اور (دیکھنا) اس نیت سے کہ جو کچھ تم نے ان کو دیا ہے اس میں سے کچھ لے لو انہیں (گھروں میں) میں مت روک رکھنا ہاں اگر وہ کھلے طور پر بدکاری کی مرتکب ہوں (تو روکنا مناسب نہیں) اور ان کے ساتھ اچھی طرح رہو سہو اگر وہ تم کو ناپسند ہوں تو عجب نہیں کہ تم کسی چیز کو ناپسند کرو اور خدا اس میں بہت سی بھلائی پیدا کردے (An-Nisa 4:19)

يُرِيدُ اللَّهُ أَن يُخَفِّفَ عَنكُمْ ۚ وَخُلِقَ الْإِنسَانُ ضَعِيفًا
خدا چاہتا ہے کہ تم پر سے بوجھ ہلکا کرے اور انسان (طبعاً) کمزور پیدا ہوا ہے (An-Nisa 4:28)

إِن تَجْتَنِبُوا كَبَائِرَ مَا تُنْهَوْنَ عَنْهُ نُكَفِّرْ عَنكُمْ سَيِّئَاتِكُمْ وَنُدْخِلْكُم مُّدْخَلًا كَرِيمًا
اگر تم بڑے بڑے گناہوں سے جن سے تم کو منع کیا جاتا ہے اجتناب رکھو گے تو ہم تمہارے (چھوٹے چھوٹے) گناہ معاف کردیں گے اور تمہیں عزت کے مکانوں میں داخل کریں گے (An-Nisa 4:31)

May Allah (SWT) guide believers towards the rite path and remove the burden of confusion that we face in adjusting His will in modern world (aamin).

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The precondition for existence of a higher humanity is not the state, but the nation possessing the necessary ability.