I was very good at most subjects in school, not because I had any particular aptitude in them, but because normally on the first day of school they'd hand out schoolbooks, and I'd read them.
Usually with these types of structures you'd have not because/ but because with the latter clarifying why in once single sentence.
With this example it ends with – hand out schoolbooks, and then adds that the writer had read them.
Is this ok grammatically?
I'd have written it: they'd hand out schoolbooks which I'd already read.
Best Answer
I suspect you are misinterpreting the word "read" near the end of the sentence. "I'd read them" could mean "I had read them" with "read" pronounced like the color "red."
From the context, "I'd read them" should be interpreted as "I would read them" with "read" pronounced like the type of plant "reed." The overall meaning is "I did well in school because I chose to read the schoolbooks as soon as I received them, beginning the first day of school." The implication is that other students did not read those schoolbooks. The overall emphasis is explaining why I did well in school.