I often incorporate stress training into my classes as it is very important for intelligibility (as better awareness of stress placement will give students clearer speaking and better listening skills). However, I am wondering whether it is worth bothering with secondary stress placement (eg. for words like 'recommend' that have primary stress on the third syllable but secondary stress placement on the first syllable).
I normally indicate stress placement with simple symbols (eg. recommend = ooO). I have seen visual language that shows both primary and secondary stress (so shapes of different sizes) in methodology books but never seen any teachers actually use these.
As far as I can tell, secondary stress placement is more or less ignored in the ESL world. It is hardly mentioned in the most prominent ESL texts (barely mentioned in Sound Foundations by Underhill or How to Teach Pronunciation by Kelly). Could this be because secondary stress placement is so inconsequential that the topic doesn't warrant much focus? If anyone has any insight on what proportion of words have primary+secondary stress, or the potential for loss of intelligibility if secondary (not primary) stress is misplaced, would be interested to discuss!