Yes, a quarter of million children were at home self-isolating last week. What do you suggest? Should there be no attempt to reduce infection?
This is why it is so important that community transmission is brought right down and why there must be an investment in good classroom ventilation and masks should continue to be worn.
Most of the north west and north east now has incidence rates of over 1 in 500 and nearly all of the rest of the country (including the south west) has an incidence rate of over 1 in 1000. Some areas are as high as 1 in 200. In a secondary school of 2,000 pupils, that could mean that there are 10 infected pupils every day. The Delta variant is highly transmissible and could mean that one infection could seed dozens of others. There is almost no mitigation in schools. It's no wonder that 25% of all new infections are in secondary age children. Even if they don't have severe symptoms, some of them will suffer Long Covid, possibly for many months. Not only that, but there are vulnerable staff working in schools and it's now known that some of them could be infected, even if they are vaccinated.
Giving the virus a good talking to and explaining that education is important won't work. Thousands of healthy children could end up with a very nasty long-term symptoms.