Although there may be differences because situations vary, there are common characteristics in children with mental retardation issues.
They have difficulty remaining focused. They have difficulty with attention and they look around the room. Keep reminding them to look at you. This focuses them back on you and what you are saying. Remind them gently that looking at the person that is speaking is paying attention to the person that is talking
They will have difficulty staying on task with things they do not enjoy (eg homework, chores, etc). Gently redirection back to the task, while making sure that they are looking directly at you when you make this redirection will be important.
They will tend to hear as much when not looking directly at you because they are not attending to what you are saying. Their attention is divided between what you are saying and whatever they are looking at.
Children coping with mental retardation issues have difficulty with both expressing themselves and understanding what is being said to them. Furthermore, they get frustrated and confused when they can not express what they want to say. Tell them that it's okay, slow down, take a deep breath, and start over. Be patient. They may have difficulty understanding:
directions or procedures
complex sentences or instructions
abstract concepts – very concrete and focused on the here and now
It is important to recognize that the things you say may need to be repeated several times and in several different ways. Give one instruction at a time. When they complete that instruction or understand that one concept, then give the next instruction. They are likely to only be able to handle one instruction at a time.
Sometimes they will use words that they have heard before without knowing what they mean, because they are mimicking others. This is natural. Ask them what the word means. Help give them verbal language.
They may use pronouns (I, you, me) inappropriately, and it will be up to you to help them to figure out who they are talking about.
They may answer questions that you feel are beyond their ability level. But do not resist answering them. They will notice, and this will frustrate them too. Do your best to bring it to their level and not make your answer too complex.
The rigid though processes of mentally retarded children make it difficult to learn from mistakes. This can result in counter-productive behaviors. They have problems with generalizing and need help with taking one situation and using the information from that situation for the other situations. For example, when learning about social skills, I would work with one skill until they learn that skill. Then I add a skill until they learn the new skill. Then I add situations until they can add situation themselves without cuing. The more difficult the task, and the more effort involved, the more difficult they are going to have, the more the task is going to be divided into smaller pieces.
Repetition is the key here. When you teach a social skill or an anger management skill, repeat the different scenarios over and over, take a break, then do it all over again. The next week, repeat the process. Think about when you had to learn your multiplication tables. You repeated them over an over. The information needs to be repeated over and over.