(1) In the case of a school at which one or more (but not all) relevant subjects are taught (wholly or mainly) through the medium of English to any age group of pupils at the school, an alteration to the school such that the number of relevant subjects taught to pupils in that age group which are taught (wholly or mainly) through the medium of Welsh would be increased or decreased by–
(a) 3 or more, in the case of age groups of pupils who are in the first key stage and age groups of pupils who are in the second key stage, or
(b) 4 or more, in the case of age groups of pupils who are in the third key stage and age groups of pupils who are in the fourth key stage.
(2) In the case of a school at which one or more (but not all) relevant subjects are taught (wholly or mainly) through the medium of Welsh to any age group of pupils at the school, an alteration to the school such that the number of relevant subjects taught to pupils in that age group which are taught (wholly or mainly) through the medium of English would be increased or decreased by–
(a) 3 or more, in the case of age groups of pupils who are in the first key stage and age groups of pupils who are in the second key stage, or
(b) 4 or more, in the case of age groups of pupils who are in the third key stage and age groups of pupils who are in the fourth key stage.
(3) In the case of a school at which there is any age group of pupils who are taught (wholly or mainly) through the medium of English every relevant subject which is taught to pupils in that age group, an alteration to the school such that–
(a) 2 or more of those subjects, in the case of age groups of pupils who are in the first key stage and age groups of pupils who are in the second key stage, or
(b) 3 or more of those subjects, in the case of age groups of pupils who are in the third key stage and age groups of pupils who are in the fourth key stage, would be taught (wholly or mainly) through the medium of Welsh to pupils in that age group.
(4) In the case of a school at which there is any age group of pupils who are taught (wholly or mainly) through the medium of Welsh every relevant subject which is taught to pupils in that age group, an alteration to the school such that–
(a) 2 or more of those subjects, in the case of age groups of pupils who are in the first key stage and age groups of pupils who are in the second key stage, or
(b) 3 or more of those subjects, in the case of age groups of pupils who are in the third key stage and age groups of pupils who are in the fourth key stage, would be taught (wholly or mainly) through the medium of English to pupils in that age group.
(5) In the case of a school at which any relevant subject is taught to any pupils (wholly or mainly) through the medium of English, an alteration to the school such that all pupils at the school would be taught all relevant subjects (wholly or mainly) through the medium of Welsh.
(6) In the case of a school at which any relevant subject is taught to any pupils (wholly or mainly) through the medium of Welsh, an alteration to the school such that all pupils at the school would be taught all relevant subjects (wholly or mainly) through the medium of English.
(7) For the purposes of this paragraph, the following are relevant subjects–
(a) religious education, and
(b) the subjects other than English and Welsh which are foundation subjects, within the meaning of section 354 of the Education Act 1996, in relation to one or more key stages (whether or not they are foundation subjects in relation to the pupils concerned).
(8) For the purposes of this paragraph–
(a) “age group of pupils” means an age group of pupils who are normally taught together in an ordinary teaching session; and
(b) “ordinary teaching session” does not include a school assembly or other school activity conducted with large groups of pupils, and references to key stages shall be construed in accordance with section 355 of the Education Act 1996.