Simple Past or Past Perfect for describing "first time" experience

Could someone please explain the difference between simple past and past perfect for describing a first time experience? For example:

That was the first time I had done that.
That was the first time I did that.

I get the feeling that the past perfect implies a relation to a later action such as "That was the first time I had done that (but I wont do it anymore)" or "That was the first time I had done that (and I will continue doing it)". On the other hand the simple past doesn't imply anything and simply states a fact about a past experience.

However, I am having trouble explaining this to a student. Can someone please explain the grammatical difference? Thank you in advance.

We've had discussions about this before. If I remember rightly, there is a definite BrE vs AmE difference.

In BrE, we would say "This is the first time I have [ever] done this", "That was the first time I had [ever] done that".

In AmE, however, I believe they favour "This is the first time I did this", "That was the first time I did that".

The BrE version doesn't imply anything at all as to whether the person won't do the action again or will continue to do it. An AmE speaker will have to say whether the AmE has any such implication.