I devote two lessons to phonetic symbols and I my pupils study all of them (the whole phonetic chart) and we have a guess game. I tell the symbol and they need to draw or to show it in the chart. Every lesson my pupils try to read new words, and I try to make it a funny game. So they feel more confident when seeing a new word in the dictionary very soon ))

I'm a university teacher and deal with students whose major is English.They're supposed to know phonetic symbols when they enter the university but it's not always so.That's why and due to a range of other reasons (mainly pronunciation drill) we've got a phonetic fortnight.So during first two weeks we practise only phonetics with our freshmen and surely we teach them phonetic symbols as well.
I suppose it's utterly important and should be taught at school regularly during first two years because English with its lack of reading rules can be a real challenge without knowledge of transcription.

I do, as the syllabus requires it. My young learners get confused, because letters and phonemic symbols are introduced simultaneously in the textbook. Also, as the syllabus is very demanding, I'm afraid too little time is spent in drilling them. So I try to do it during the whole (first) year.

I remember clearly the symbols and transcription notes my teacher used for teaching us to read and to pronounce English letters to make up English words. I think essential principles of phonemic script must be taught; the formation of letter combinations and so on.  

Besides it also depend on the sound system of a student’s native tongue. In some languages there is a lack of many English sounds, and for understanding its pronunciations they should learn phonemic script of the corresponding letters.

Besides, nowadays there are so many audio texts that will be useful and more productive for our students.

In one word I think essential principles of phonemic script should be taught at an early age just for the beginners. 

You are welcome