Face coverings will be mandatory for staff and students in Year 7 and above in areas that are subject to local lockdown. Currently in Tower Hamlets - which is not subject to a local lockdown - it is the choice of individual schools. In either case, it is unlikely that they will be worn in a classroom, instead they will be worn when moving around the school, where social distancing cannot be maintained.
Check with your school to understand what they are asking you to do. The new rules do not apply to primary schools where the risks to children are lower.
Read more on the Department for Education blog: Face covering in schools and colleges: your questions answered or read the full guidance.