I've never been to any English schools in my life nor had anybody to guide me through the learning process. My self-assessment has always been related with comparing and contrasting native English speakers' speech to my own speech. Shadowing natives has helped me quite a lot, not only with my speaking skills but also with my listening skills. As for my writing, well, at the beginning I used to copy short texts and memorized them until I had them engrained in my mind and then I could notice that my vocabulary increased day after day. Needless to say that I read lots of grammar books in order to understand how the English grammar worked. At present, I assess my listening skills by watching American movies without subtitles. Whenever I come across idiomatic expressions or slang, I jot them down quickly (I'm talking about the sound of slang and idiomatic expressions) so that later on I can look them up. As time goes by, I realize that my listening and speaking skills are getting better and better.
To wrap this up, I must say that I've always bent over backwards to keep my English polished. Nevertheless, I know that I still have a long way to go since I keep making mistakes when it comes to writing.
I watch or just listen to programs in my target language and find I can understand more and more.
I speak with others in my target language and find I can express things I could not previously express. Whether the others are teachers or language partners, they tell me that they see progress. It is probably actually easier for those who do not speak with me often to see the progress than it is for me to see it.
why do you think that measuring progress when you study on your own is different from when being taught by a teacher?
In fact, it is certainly the same. Learners can see (or should see) their progress despite the way they learn. If you understand more than a few months or years ago, you definitely make progress. Or, you can take an exam such as IELTS regularly.
The question is, what way is more effective?
Usually, it's tests....
Or recordings if we're talking about speaking parts... You can record yourself every week , and then once just listen all the recordings...