If someone hasn't been exposed to the sounds of a foreign language during their early childhood, it will be difficult for that person to accurately hear and produce those sounds later in life. Difficult but not impossible. That's why ESL students need practice listening to specific sounds that don't exist in their native languages. If they listen to entire conversations, they probably won't be able to pick out and focus on the individual sounds they need to work with. That's why they need focused listening practice: just listening to -th- sounds, for example and just comparing -th- to the sounds the students been substituting. The more the student can listen the better, and that means outside of class too. They need to listen in a way that tests their listening accuracy. Did they hear "sick" or "thick"? Students will think they hear it correctly, but when you test them and ask which one you said, they often get it wrong. This sound discrimination component of their education can take a lot of time in the classroom.
So they need a way to test themselves when practicing alone and still get instant feedback. Look for minimal pairs sound discrimination software. Speech therapists use these. However, speech therapy students tend to confuse different sounds than English learners would, so look for minimal pair sound discrimination software that is just for ESL learners, preferably designed for the language background of the student in need. That way, the practice sounds will be the ones the student actually needs to work on. Even computer software is not always so convenient. Try looking for mobile phone apps that test students on listening to minimal pairs. The iTunes App Store has some American English Pronunciation apps that are geared toward specific language backgrounds, and they are only 99 cents. Some are free. With these, students can practice their listening and get instant feedback any time of day, whereever they are. Practicing a few minutes several times a day is very effective!