imperfecto vs pretérito

Question

In the example sentence. "Nos felicitaron porque habíamos aprobado todo con una nota alta," why is haber in the imperfect? I think of passing or failing something as something that happens in a moment -- you receive your grade and either it is pass or fail -- not as an ongoing state of being. Could one say "hubimos aprobado" or would that be wrong?

Answer

Hola R,
the pluperfect tense, in Spanish, "El Pluscuamperfecto" is formed by haber in El Imperfecto (había, habías, había, habíamos, habíais, habían) + the past participle of the main verb. 
The formation of "had happened" with the preterite of haber: "hube, hubiste, hubo..." is called "El Pretérito Anterior", and it is rarely used nowadays, at least in spoken Spanish. The use of the pluperfect tense with "había" is generalised, even when it is talking about actions that may sound as very precise in the past. 
If we want to express that precision in time we are more likely to use some other structure, like:
Tan pronto como llegamos (~cuando hubimos llegado) 
Nada más llegamos (~cuando hubimos llegado)
En cuanto llegamos (~cuando hubimos llegado)
I hope this clarified it.
Saludos
Inma

Answer

It certainly helps to know that there's a tense nobody uses so I don't have to learn it! I don't think I quite understand how I would form a sentence with your alternate suggested phrases.

Answer

Here are some sentences using the alternatives:

Nada más llegamos al aeropuerto, nos dijeron que el vuelo estaba cancelado.
As soon as we arrived at the airport, they told us the flight was cancelled.
Tan pronto como nos sentamos para descansar, nos quitamos las botas.
As soon as we sat for a break, we took off our boots.
En cuanto lo vi, empecé a temblar.
As soon as I saw him, I started to shake.

These, used with El Indefinido are what we would use instead of saying "Cuando hubimos llegado, cuando nos hubimos sentado, cuando lo hube visto"
Saludos
Inma