Pakistan has about 17,000 religious schools, or madrassas, which provide children with free religious education. br This means they have to memorise the Koran from as young as five-years-old. br There are nearly 2m students enrolled in Paksitan's madrassas. br But a 911 commission report in the US dubbed them as as "incubators for violent extremism". br BBC Urdu's Asif Farooq explains the increase in their popularity.