Lochhead's poem is set in the 1980s and its primary themes are disparity in wealth, family dynamics, and how friends grow apart when differences in wealth and status eventually emerge.
Consider the speaker's first stanza:
We were first equal, Mary and I
with same coloured ribbons in mouse-coloured hair
and with equal shyness,
we curtseyed to the lady councillor
for copies of Collins’ Children’s Classics.
First equal, equally proud
But that happy feeling of being totally equal does not last long. As the school year progresses, the competition between the two best friends, ramps up as they vy for the "top desk" at their private school (the "lady councillor" indicates that they attend a private, likely Catholic school) and the speaker fears her friend's "superiority at sums." (Mary is better at math.)
The two girls go home to nearly identical houses as far as structure, but the interiors, the "homes," will shape the choices of the poem's title.
The speaker's friend's family decides to move away:
Something about a three-apartment
and a cheaper rent.
But on her way to school, from a top a two-decker bus, the speaker sees Mary's father flanked by "elegant greyhounds" (this breed of dog is symbolic of the elite lifestyle). The speaker juxaposes this sight with her knowledge of how her friend's father
didn’t believe in high school education,
especially for girls,
or in forking out for uniforms
"Especially for girls," of course, has weight. In the father's estimation, education for girls is considered frivolous. The young speaker seems to feel some sorrow for her friend and the choices that were thrust upon her.
Fast forward ten years, and on a bus, the speaker runs into her friend and her husband
who is tall,
curly-haired, has eyes
for no one else but Mary.
The speaker says, "you can see where the attraction lies." And her claim "not that I envy her, really" sounds a bit hollow.
The speaker exits the bus with her "arms full of books" and reflects on the fact that choices were made in those early teen years.
...when the choices got made
we don’t remember making.
Mary has married and seems happy. The speaker has pursued higher education and though it is not overtly stated in the poem, it is implied that she has remained single. While Mary is happy and there is only a twinge of regret from the speaker (again, in the line "not that I envy her, really") about her own life, she does think about how those "choices" may not have been their own at all, but shaped and guided by forces beyond their control.