Some words below that you might find useful in your letter:
From the Children's Rights Alliance :
Under the Equality Act 2010 schools must not discriminate against, harass or
victimise pupils because of their sex, race, disability, religion or belief, sexual
orientation, because of a pregnancy or maternity or because of a gender
reassignment (these are called “protected characteristics”). Schools must
also have due regard to the need to eliminate discrimination and should make
sure that their behaviour policies do not unintentionally discriminate against
pupils by unfairly increasing their risk of exclusion.
Under the UN Convention on the Rights of the Child the government must ensure
that ‘school discipline is administered in a manner consistent with the child's
human dignity and in conformity with the present Convention’ (Article 28(2)) and
that education shall be directed to ‘…The development of respect for the child's
parents, his or her own cultural identity, language and values, for the national
values of the country in which the child is living, the country from which he or she
may originate, and for civilizations different from his or her own’ and ‘…The
preparation of the child for responsible life in a free society, in the spirit of
understanding, peace, tolerance, equality of sexes, and friendship among all
peoples, ethnic, national and religious groups and persons of indigenous origin..’
(Article 29(1)(c) and (d)). Unlike the Human Rights Act, these rights are not part
of English law but should nonetheless be considered by courts and public bodies when making decisions.