Meaning of Shell, Remove, and Hundreds in Alice Winn's In Memoriam (and other novels with public school settings)

Question

Alice Winn's In Memoriam (2023) is partly set in an English public school around the outbreak of World War I. Toward the beginning of the novel, the narrator states:

Preshute was a younger public school, and eagerly used the terminology of older, more prestigious institutions: Shell for first year, Remove for second, Hundreds for third, followed by Lower and Upper Sixth.

Despite having read other books with a similar setting, I have not encountered these terms before. The exception is Remove: I recall that in the Billy Bunter stories, the eponymous, bespectacled protagonist is called "the owl of the Remove". My understanding from reading those, probably mistaken, was that Remove referred to a group of schoolboys who needed to resit some exams and so were "removed" from what would have been their class year had they passed the exams on their prior attempt.

I also can't quite figure out the mapping between the years, the forms, and the students' ages. I thought that public schools admit students into first form at around age 12 (so that most students would turn 13 during their first year), and that students complete sixth form (and their A-levels) at around age 18. But there are apparently "lower" and "upper" forms? Cursory googling confirms that there exists an Enid Blyton novel called Upper Fourth at Malory Towers, but Preshute doesn't appear to have an Upper Fourth, or indeed, any fourth or fifth forms at all.

So here are my questions. They seem like a lot, but they are all about understanding how "Shell", "Remove", and "Hundreds" are used at Winn's fictional school, Preshute:

• Around 1914, how many academic years comprised a public school education, six or seven?
• Has this changed in the intervening century?
• What are the "older, more prestigious" schools that Preshute emulates by using the terms Shell, Remove, and Hundreds?
• Why those particular terms? For example, hundreds of what?
• Were those terms consistently used across those schools? I.e., is "Remove" always the second year?
• Did Remove ever have the sense I thought it did, of students held behind due to unsatisfactory academic performance?
• What are "lower" and "upper" versions of a form? Are they one school year apiece? It cannot be that every form has a "lower" and an "upper", because that would mean one's public school education takes twelve years.
• Does any or all of this vary from school to school? So for example, school A might have a lower and upper fourth, while school B has only one fourth form, but a lower and upper sixth?
• Generally, what age would a student be in any given form?
• What happened to the fourth and fifth forms at Preshute?

Without this information, it's a bit confusing trying to understand what's going on in In Memoriam. For example, some interactions might be read as mildly disturbing or entirely horrifying depending on how close together or far apart in age the two students are. Thanks!

Answer 1

The OED gives this for ‘Shell’

The apsidal end of the school-room at Westminster School, so called from its conch-like shape. Hence, the name of the form (intermediate between the fifth and sixth) which originally tenanted the ‘shell’ at Westminster School, and transferred of forms (intermediate between forms designated by numbers) in other public schools; see quote

1857 The lower fifth, shell, and all the junior forms in order [at Rugby]. T. Hughes, Tom Brown's School Days i. v. 111Citation details for T. Hughes, Tom Brown's School Days

1877 The noise grew louder and louder, until the birch was safely deposited in a small room behind the ‘shell’,—so the upper end of the room was called from its shape [Westminster]. W. P. Lennox, Celebrities vol. I. 43Citation details for W. P. Lennox, Celebrities

1884 The Headmaster faced all the boys excepting the tenants of the ‘Shell’. F. H. Forshall, Westminster School 3Citation details for F. H. Forshall, Westminster School

1903 The third ‘shell’, a form within measurable distance of the lowest in the school [Harrow]. Blackwood's Edinburgh Magazine June 742/2

For ‘Remove’ it gives

6. Esp. in early use chiefly with reference to certain British public schools, esp. Eton College. 6.b.1718–Frequently with capital initial and with the. (The name of) a form between the Fourth and Fifth year, itself sometimes divided into the Lower and Upper Remove; (also) a class or division within another year (esp. the Fourth year); (in modern use also) spec. a class in which pupils spend an additional year preparing for examinations. Now chiefly historical.

In later use frequently associated with the fictional schoolboy character Billy Bunter, the ‘Owl of the Remove’ at Greyfriars school, in the novels by ‘Frank Richards’ (C. H. Hamilton 1876–1961).

1718 The successive forms were called..First Form, Lower Remove, Second Form,..Fourth Form, Remove, Fifth Form. in H. C. Maxwell-Lyte, Hist. Eton Coll. (1877) 288Citation details for in H. C. Maxwell-Lyte, Hist. Eton Coll.

With regard to Upper and Lower forms, under ‘form’ the OED gives:

I.6.b.1560–spec. One of the numbered classes into which the pupils of a school are divided according to their degree of proficiency.

In English Schools the sixth form is usually the highest; when a larger number of classes is required, the numbered ‘forms’ are divided into ‘upper’ and ‘lower’, etc. The word is usually explained as meaning originally ‘a number of scholars sitting on the same form’ (sense II.17); but there appears to be no ground for this.

I’ve as yet not tracked down a form named ‘Hundreds’, if I find anything I’ll add later.

As to which schools, there are several named in the various definitions and quotations above.