NOT A TEACHER
(1) I think that in real life, your two sentences are interchangeable. That is, native
speakers would understand either sentence.
(2) But if you are interested in speaking "perfect" English, then I think that there is a
(a) so = therefore.
(i) I am poor, so I cannot visit your country.
(b) so that = purpose/ result
(i) I always drive to work early so that I can get a good parking space. (purpose)
(ii) I drove to work early, so that I got a good parking space this morning. (result)
(Notice the comma. In speech, you need to pause.)
I wish to credit the great Professor George O. Curme for explaining the two different
meanings of "so that."
(3) Regarding your sentences, it is only my opinion:
I have to learn driving so that I can drive my own car. (The purpose of my learning.)
I learned how to drive, so now I can drive my own car. (Therefore)
I learned how to drive, so that I am now very popular with my neighbors, who want
me to drive them everywhere! (The result of my learning.)
Student or Learner