My son forgets to write in planner homework assignments. When he does homework, he looses it before he turns it in to teacher.
Depending on the underlkying causes of your sons dyslexic symptoms, he may have a poor working or short term memory.
If your son has a poor auditory memory, then he will have problems remembering sound based input. and this would include verbal instructions.
So he would require writen back up of his home work tasks from school. In some instances if your son has a very poor working memory the school may have to provide you directly with say a weeks work of his homework tasks.
Depending on whether this is a Visual or Auditory memory deficit will determine which are the best coping strategies to adopt. If your son has say a poor Auditory memory you may find that he has developed a very good visual memory, in which case creating visual coping stategies would help.