It depends entirely on the school. Ours treats children who are non-Catholic as if they were in the process of Conversion. They are required to attend all Masses, participate in religion class, and prepare for and participate in the Sacraments just like their RC classmates, except that they can choose not to go through with Confirmation (as can any student.) Essentially, if they go along completely and finish 8th grade, they *are* RC when they leave, at least technically, because of the Confirmation with the school as parish of record.
This is undoubtedly because they only started accepting non-Catholics in the past two years; our previous school was a lot less secure in terms of enrollment and had been accepting non-Catholics for decades, they were a lot more accepting and only required participation in religion classes. Our current school still does not accept non-Christians unless they are willing to participate fully and to be baptised in some Christian church before starting school.
As parents, we have to sign paperwork agreeing to all of the religious requirements, including regular weekly Mass attendance with the family (that's on the honor system; they don't take attendance on Sundays.)