“I'd been doing my English homework for 30 minutes when my friend called last Saturday.”

WHEN TO USE IT: The past perfect progressive (also called the past perfect continuous) is used to indicate that a continuing action in the past began before another past action began or interrupted the first action.

FORM: [‘had been’ + present participle]

Each of the highlighted compound verbs in the following sentences is in the past perfect progressive tense.

The toddlers had been running around the school yard for ten minutes before the teachers shooed them back inside.

Here the action of the toddlers ("had been running") is ongoing in the past and precedes the actions of the teachers ("shooed") which also takes place in the past.

We had been talking about repainting the front room for three years and last night we finally bought the paint.

In this example, the ongoing action of "talking" precedes another past action ("bought").

A construction crew had been digging one pit after another in the middle of my street for three days before they found the water main.

Here, the action of digging ("had been digging") took place in the past and occurred over a period of time. The digging was followed by the action of finding ("found").

Madeleine had been reading mystery novels for several years before she discovered the works of Agatha Christie.

In this sentence the act of discovery ("discovered") occurred in the past but after the ongoing and repeated action of reading ("had been reading").

The chef's assistant had been chopping vegetables for several minutes before he realized that he had minced his apron strings.

This sentence is a bit more complex in that it contains three different past verb tenses. The sequence of tenses conveys a complex set of information. The past perfect progressive ("had been chopping") is used to emphasise the ongoing nature of the past act of chopping. While a second past perfect progressive ("had been mincing") could be used, the past perfect ("had minced") is used to suggest that act of mincing was completed. The simple past ("realized") is used to describe the action closest to the present, an action that followed both the chopping and the mincing.