I was reading To Kill a Mockingbird and I came across a sentence:
This was the first {time} he had let us know he knew a lot more about something than we thought he knew.
I can't understand the usage of past perfect in the second clause (he had let us know). Past perfect is used when one action occurs before another in the past. This much I know, but in this case the occurrences are pretty much simultaneous.
Compare the past tense versions...
1: That was the first time I had done it
2: That was the first time I did it
...with the corresponding present tense versions...
3: This is the first time I have done it
4: This is the first time I do it
Although #1 is probably the more common (perhaps even "more correct") version of the first pair, most native speakers wouldn't particularly notice anything unusual about #2. But native speakers would never use #4 - which is a very common error among speakers of certain other languages, so even if the speaker had a perfect English accent, the assumption would be "non-native speaker".
I think the reason we require Present Perfect (essentially, a Past form) in the second pair is because semantically there's an implicit reference to the past (all the time before "now, time of speaking", during which I hadn't done it). But because we're already in the past with the first pair, it seems unnecessary (but not actually "incorrect") to specifically distinguish between "past" and "even earlier past".
Bear in mind that as a general principle, native speakers will normally tend to avoid the additional complexity of Past Perfect if they don't feel they obviously need it.
"This was the first time he let us know..." could suggest that there were other subsequent times when that happened: a second time, a third time, etc.
The past perfect in "This was the first time he had let us know..." does not reflect past before past but is the past form of a life experience: up to then, he had never let them know. It's easier in the present:
If backshifted, "has" becomes "had":
