OK, latest update in the saga...
I contacted the Equality Authority, detailing our situation. This is part of their response:
An educational establishment shall not discriminate in relation to -
a) the admission or the terms or conditions of admission of a person as a
student to the establishment,
b) the access of a student to any course, facility or benefit provided by
the establishment.
c) any other term or condition of participation in the establishment by a
student, or
d) the expulsion of a student from the establishment or any other sanction
against the student.
If you feel that your son has been unfairly treated you could lodge a
complaint by first notifying the person/organisation against whom the claim
is being made,within two months of the date of the most recent occurrence
of the discrimination (using an ES1 and ES2 form, which can be obtained or
downloaded from the Equality Tribunal website).
I was under the impression that points a) through d) weren't applicable to schools who were allowed discriminate on the grounds of religion? Has anyone any experience of lodging a complaint as per their suggestion?
As always, many thanks for your advice and support: this is an invaluable support community for me at present!