New rules from the Education Ministry of the Islamist Hamas movement ruling the Gaza Strip will bar men from teaching at girls' schools and mandate separate classes for boys and girls from the age of nine.
The law, published on Monday, would go into effect next school year and applies throughout the coastal enclave, including in private, Christian-led and United Nations schools.
Critics of the new measures say the Islamist movement is trying to force its ideology on society, but proponents say they merely want to codify conservative Palestinian values into law.
"We are a Muslim people. We do not need to make people Muslims, and we are doing what serves our people and their culture,'' Waleed Mezher, the Education Ministry's legal adviser, told Reuters.
Hamas has administered Gaza since fighting a brief civil war with its Palestinian rivals in the secular Fatah party in 2007, a year after it won a surprise majority in Palestinian parliamentary polls.
The political split paralyzed the legislature and mostly prevented the passing of new laws in Gaza and the West Bank.
But Hamas parliamentarians in Gaza acted alone to approve the new education law, and the movement's critics have for years accused it of trying to build a separate state in Gaza.
Zeinab Al-Ghoneimi, a Gaza activist for women's rights, said the new law was part of a Hamas project to impose its values on Gaza residents.
"To say that the old law did not respect the community's traditions and that they [Hamas] wanted to reform people now is an insult to the community,'' Ghoneimi told Palestinian radio.
"Instead of hiding behind traditions, why don't they say clearly they are Islamists and they want to Islamize the community,'' she said.
Private and Christian schools, where classes are mixed until high school, would be the most affected by the decision. Gaza's government-run schools were already mostly gender-segregated.
The Gaza Education Ministry said the private schools had been invited to discuss the legislation before it was enacted but failed to do so.
Hamas leaders have repeatedly denied accusations by human rights groups they are trying to impose Islamic laws on Gaza.
Rights activists have criticized moves by Hamas's government in recent years to impose Islamic dress on female lawyers and school girls, ban men from working as hairdressers for women and interrogate couples walking in Gaza's streets.