As the chart indicates the main factor that prevent the students to follow a conversation , about half of the students consider fluency the main factor that prevent them to follow a conversation . So It is may be a good to study phonetics rules such as intonation , I simulation, pausing ....etc . They also may need to practice speaking English between each other continuously.
The second factor is pronunciation as about 33% of the students find that pronunciation is a factor which disable them during speaking . So it is suggested to use media during their classes as audio tapes or videos in order to improve their pronunciation and listening skills as well. It also may be good to study some of pronunciation rules .
Grammer also is considered as the third factor that disable some of the students during speaking , so it is suggested not to focus on Grammer rules but trying to study conversational Grammer - practicing Grammer through conversation- and practicing it between each others