According to my textbook (my teacher isn't clear in her elaboration of my question), 'the /ə/ never drops out if that would result in three or more consonant sounds together. You would see this in words such as appartement, mercredi, and première. On the other hand, in words such as batterie, boulevard, and évènement it always drops out, as indicated in dictionary pronunciations, because you end up with just two consonant sounds together.
My frustration with trying to understand this is the lack of definition in what exactly is a consonant sound. Because nobody explains this, the examples given (an example of one of them being: two consecutive consonant sounds result (/ə/ sound dropped) le polo de Marie) are useless. And though I have my own theories, I'd rather jump in prepared than have only the back-up of my own speculation while treading dangerous waters. So, if anyone could help me, I'd be very, very thankful.