Unofficial Christ's Hospital Forum

In the mid-50s the forms went as follows:

(III), LF, LE, UF, GE, Deputy Grecians, Grecians. There was also a V (after GE) for people mainly retaking O-level and not expected to stay on. Almost everyone started on the LF. I'm not sure why some people were put on the Third Form, which had only one stream.
Grecians once they got their buttons were 3rd, 2nd and 1st parting (1st, 2nd, 3rd years respectively). They read grace at tea, breakfast and dinner respectively. As there were few 3rd P's (1st year Grecians mostly didn't have buttons), 2nd P's had to fill in at tea. Non-button Grecians (the great majority) were "probationary".

In about 1960 the naming was changed thus:

II, III, LE, GE (fast stream)
II, III, LF, UF, GE (slow stream)

I think there were 8 of us (aged 9) when I joined the First Form at Hertford in 1957. We were joined by a few more when we got to the Second Form (in both cases - I think? - Miss King was the Form Mistress). Then we were split into Lower Third A or Lower Third B, to be joined by all the 11plus entrants.
Regarding Elizabeth Cairncross' house on The Avenue (presumably now Mary Ireland's), it was occupied by at least two years before then by Jean Morrison who came down to Horsham when the girls moved from Hertford and she became Deputy Head for those two years. I would have no idea what the property was used for before that!