Children with special needs often have difficulty retaining what they learn and many will not remember information taught to them without deliberate practice. Deliberate practice is familiar to anyone who plays video games. A few objectives are mastered by gamers that get immediate feedback that helps them learn from mistakes and must master each objective before moving on to the next one.
Children learn academics in much the same way in order to retain what is being taught. This is not the same as drills or repetitive teaching. Those methods are teacher or parent-focused and require the child to only respond. Deliberate practice is child-centered and focuses on how the child performs on a given task with a parent or teacher there to ask him/her questions that will help improve that performance.
For example, if a child is trying to pronounce a word looking at a card with a word that ends with -at, a parent might hold up a word the child already knows, like "cat," and ask the child, "What is this word?" When the child answers "Cat!" the parent might then hold up the other word, which could be "mat," and ask the child, "How are these words alike?" and the child may realize they end the same way and understand that they also have the same sound at the end.
Of course, it's much easier just to tell your child the word when s/he doesn't recognize or know it, but if you want him/her to remember it, the above method of allowing him to use his cognitive skills to figure out the word with help from you works much better. Try reviewing words or other reading-related material with your child as s/he gets ready to return to school and provide him/her with books and other things to read.
Read with your child and point out pictures in his/her books that help tell the story and ask your child to tell you what s/he thinks is going to happen next. Also, get siblings and other family members to encourage your child to read by reading with or to him/her. Point out words your child knows when you go out and see the names of familiar places and things displayed on signs.
Making reading a part of your routine each day, whether by reading your child a bedtime story or asking him/her to read the name of the cereal on the box while preparing his/her breakfast, is an important part of your child's literacy development and should be part of your family's every day routine. Your child may not be able to learn as quickly or read as well as his/her siblings and other people, but s/he can learn to recognize some words and sounds.