You need to focus on the purpose, audience and format of the task and create a detailed plan to help you write and clear and coherent response. The purpose of the task is to persuade your headteacher to reduce homework given to pupils, the audience is your headteacher and the format is a letter.
In your plan you must write around 4- 5 points as to why pupils should receive less homework. These points need to be explained and supported with evidence. Some suggestions may be:To reduce stressTo allow time for extra curricular activities Pupils already get enough work and revision from school You need to be persuasive throughout in order for the letter to be successful and achieve your goal. Don't forget that the format is a letter so it needs to look like one. Think about how you are going to open and close the letter. Also bare in mind that this letter needs to read formally and focus on effective spelling, grammar and punctuation.