Not all deaf people know how to sign. Not all deaf students use interpreters. Some prefer to communicate through lip reading and some prefer sign language. Very few people are totally deaf. A hearing aid does not correct a hearing loss like glasses correct vision problems.
Most deaf persons have sensory neural hearing losses and the clarity of speech is affected.
Many deaf people are easily understood. Others cannot monitor the volume and tone of their speech and may be initially hard to understand. Deaf students, just like hearing students, vary to some degree in their communication skills. A deaf student's English skills are not related to intelligence but are similar to those experienced by non-native speakers of English. These terms carry a negative connotation and should not be used.