Speech therapy covers many areas including rehabilitation for loss of speech after a stroke. I’m assuming this is not the case for your student. I’m guessing the speech therapist is working on a speech impediment with your student.
I think the first step is to assess your student’s needs in the language classroom and to find out how best you can help him or her. The best way to do this is through a private conversation with the student. If the person is under 18, invite the parents along too. Gather information from the student, including: what work your student is doing with the speech therapist, which areas of pronunciation are difficult, which method of correction works best for him / her. Your student and / or the parents are a good starting point for this.
In the classroom be sensitive to your student’s spoken English and correction of his/her pronunciation errors. It might be best not to ask direct questions to this student when working as a whole class; i.e. don’t have him / her speak in front of others unless (s)he volunteers. An alternative opinion is that the student should be treated the same as everybody else. You can trust your own judgement on this one based on your knowledge of the extent of his difficulties.
You don’t say if you are working alone or as part of a school. If possible, talk to your director of studies who might be able to give you support or ideas. If you have the time, try to speak to a speech therapist, preferably the one working with your student. Try to read a good book on pronunciation; for example, Sound Foundations by Adrian Underhill.
If you want advice on more specific areas, please feel free to write in again.