There is a nice poem in Bengali by Tagore about discovery of shoes, one king once thought "I am the king, and I have so much dirt on my feet!", he ordered for a prompt solution and the advisors came up with the brilliant idea of covering the entire kingdom with leather! The work started accordingly, after wasting a lot of cattle and money they realized that it would be a futile effort, king was sad. And then an old man from the villages visited the king and said he can help. King was amused, but he agreed. Then the old man took the measurement of the king's feet, and made a leather cover for his feet; and shoes were invented!!
There is no effective way to control **** on internet even after spending huge resources, there will always be a way around and teens will be the first to figure that out, social media will help in spreading the new found tricks. Far better method is individual monitoring by parents and school, don't give kids access to internet on mobile, keep the computers in open area, install password protected parental control software and screenshot recorder to check what the kid is surfing, most internet security softwares come with this feature, they are cheap, some are even free. This method is effective, costs less, and easy. Btw, internet plans are far more costlier than Rs.5-10 DVDs, imagine how much data one single DVD can carry, kids can rent them and copy them also, how do you stop it without personal monitoring?