Hi Maureen,
 
It is so hard to see your child struggling.
 
Here are some things I would suggest you could do.
 
If you have a reading specialist in your school or in your school district, I would suggest that you ask to have an academic assessment, to pinpoint exactly what level your son is reading at, and what specific areas he's having difficulty with.  Ask for a parent debriefing after the assessment is done, so that you and the school can work together to help him.
 
If he's having difficulty figuring out how to pronounce words, then I suggest that you look at my website:  www.dynamicreadingandwriting.com, to see if he has phonological awareness difficulties.  This means that he's not hearing sounds clearly enough to help him match what he says to what he sees when he reads.  This isn't a hearing difficulty, it's a perception difficulty, and there are ways to help children who have this problem.
 
If he can read his grade three words correctly, but doesn't understand the material, then I suggest that you make sketches of the material with him.  That way he can organize, remember, and understand the information, using visual cues.  We learn visually and verbally, but, if children are having difficulty understanding what words mean, then we can translate the words into pictures, and children get meaning that way.
 
Is there a resource teacher in the school your son attends?  If he could have some in-school tutoring in his specific areas of weakness, that would be very helpful to him.  If your school doesn't have a pull-out resource room, then perhaps you could secure a private tutor for him.  Some school districts have Saturday classes for students who need help in specific areas, at a minimal cost.  If this isn't available to you, then perhaps your school would know some retired teachers who may come to the school to help children, or who may tutor privately.