Secondary schools are already tackling this issue as part of PSHE provision and IMO, their input should be complementary to parental discussions and guidance at home. An increasing number of Year 5 and Year 6 10/11 year olds have internet enabled devices, so this age group is not too young to be taught about internet safety, respect for eachother's bodily autonomy and the importance of treating people with dignity and respect. Exposure to porn should be mentioned alongside discussions about why games and films are age-restricted and why censors protect minors in this way.
Ideally, both parents or guardians should be discussing porn with children, but it should never be under-estimated how much impact is made when male role models take the lead in home discussions about porn; fathers, older brothers, uncles and grandfathers. It's easy for cynical teenagers especially to think that 'Mum is on her feminist soapbox again', but it's especially powerful when their Dad explains why porn can be problematical both personally and politically. It can be tricky to get this right and strike the balance between reassuring young people that curiosity is natural and nothing to be ashamed about - and protecting them from unrealistic, hateful, misogynistic and damaging images.
It's also very important to focus on the positive and engender an expectation that sex is meant to be a fun, enjoyable activity between consenting participants who treat eachother with respect. What constitutes consent is particularly crucial - and discussions about coercion and pressure that is either exerted or experienced.
As for restricting children's access to the internet, I think taking away their rights is the wrong approach and by the time they go to secondary school, is fruitless and counter-productive. Their rights to conduct a safe search have already been trampled on by the porn money-makers; taking away their rights of use compounds that abuse. Currently it would be virtually impossible for GCSE students to pass exams without internet access; Maths. relies on students' use of the MyMaths website and there are numerous revision podcasts - in addition to the research available on the web. As parents we've always found the best approach is to give them the facts and then trust them to self-monitor.
It is vital that schools discuss porn in PSHE, because some parents can't or won't raise the issues at home and young people need the best guidance from the most educated sources. One of the most important messages for boys is that it's okay not to like or use porn, or to give into peer pressure to watch it. It's often overlooked that boys are under tremendous pressure to like porn and to want to emulate the sex that is featured in it and that this pressure sometimes comes from their female partners as well as their male peers. Fortunately it is embedded in PSHE that girls are encouraged to resist sexual coercion and pressure, but boys are often overlooked in this respect.
It can be especially difficult for schools to strike the right balance, because teachers are acutely aware that some students live in homes where the adults use porn and there is potential for an adversarial conflict with the messages students are absorbing from parents, but there are some fantastic resources available to generate debate and discussion.
I agree that porn should be contextualised within a backdrop of wider societal issues such as misogyny and general unkindness towards people who don't fit societal norms but it's utterly pointless pretending that exposure to porn before a young person has become sexually active is harmless. As it is to deny the impact that porn has had on beauty practices or young people's expectations of how they should look and behave. Educating young people to follow the money and to question the exploitative nature of porn and how it suppresses sexual and personal expression rather than frees, is a particularly effective tactic. Young people are not stupid and they don't like the thought of being manipulated or exploited.