Independent and expert MHRA has approved the Pfizer vaccine as safe and effective in over-12s (so as scientists, statisticians, doctors, pharmacologists etc, they have already weighed up the benefits and risks and judged that the benefits outweigh the risks - so non-expert and non-independent Johnson, Williamson, Gove and Javid don't need to repeat this exercise).
Actually allowing over-12s to receive the vaccinations approved for them before September is key in reducing transmission and infection in schools.
It should be optional. The trouble is people who are against it for their own children feel the need to stop other people's children getting it (to ensure their own children don't miss out).
Plus stop the mass self-isolation of students with negative tests. They are not infected or infectious. Do daily testing if really necessary, but it is rather a waste of plastic, room space, time and human resources at an accuracy rate lower than 50%.