[HansTWN]

Oh, 了 LE is being used all the time. Well, you can argue either way here. I, personally, wouldn't really call it a GRAMMATICAL past tense, since only the presence of a single word turns it into past tense. Just like European languages have only remnants of tonality (tick and teak would be an example of tonal variations of the same word in English), this past tense is very, very rudimentary. Nothing changes, just a word indicates past or future. Compare adding a simple LE 了or GUO 過 to what the Germans are doing -- 5 different verb forms for each tense! As far as I am aware, in your example, the 了 only tells you that it is in the past, it is the rest of the sentence (learning being an ongoing process) that makes it clear that it is continuing into the present. Seems the present perfect is inferred rather than expressed through a grammatical construction. If you say "我去過了" "I have been there", then no relationship to the present is established with the very same structure. Of course, in Chinese you are able to get that same meaning accross without all that structural baggage! Anyway, I am no linguist, so I am just expressing my thoughts on this.

And I think grammar is best learned through reading, rather than memorizing the rules. Who has time to think about rules when speaking a language? It must come naturally to you, a simple feeling that something is right or wrong, even if you cannot recite the rule. Though a teacher should know it!