I agree with trying Allison C's plan. The two of you have developed a pattern over the years that is no longer working. Yes, he may be scared, as "Mommy" suggests and needs reassurance but, unwittingly, you have reinforced his fear by always responding for all these years. He hasn't learned how to soothe himself back to sleep because you've always done it for him. And......here is a subtle thing that is happening. Because you always respond he, at some level, feels that there must be a reason to feel fearful. If you were confident that he could handle waking up and being by himself he would be more confident in his ability to go back to sleep.
I suggest that you talk with him about why he wakes up, reassure him that you are always in your bedroom and you'll always protect him if fear is what is causing him to scream/cry. Your presence in the house is his protection. Sympathize with his fears whatever they are. Allow him to talk about whatever is causing him to wake up and scream for you. This may take some time because it's become a habit and he may no longer be consciously aware of why he does this.
There are books about sleeping. You can find them at the library. Ask the librarian. Or go to a book store. Read those together. They may suggest ways of getting back to sleep as well as other conditions. Problem solve together about ways he can get himself back to sleep or soothe himself when he's upset.
Some suggestions are to give him a flashlight. My adopted daughter came to me at the age of 7 with a plastic doll like toy that lit up when you squeezed it. This helped her when she was living in a children's home and was scared and felt alone. I've seen flashlights that are in the shape of animals. Perhaps he could have a radio or CD player that was set at a low sound level that he could turn on. Or a night light that is either left on all night or that he could turn on.
Another suggestion is to teach him a short prayer. I remember saying one that my mother had taught me to say to myself when I was a child and woke up scared. She did this by coming in to me or taking me back to bed and sitting with me while I talked about what had scared me. Then we would say the prayer together and she would leave. She did this gradually. I was probably 5 and our family life was insecure with not enough money and my parent's fighting. She started by sitting with me while I was in my own bed and listening to me until I ran down and fell asleep. Then she taught me the prayer and stayed with me while I said it. Then she would come in, remind me about the prayer, tuck me in again and leave. And then I was able say the prayer on my own and fall back asleep without calling for her. She told me that this was the goal; for me to be able to get back to sleep on my own. She was calm and patient. I don't remember how long it took.
You may think of other techniques to teach him to help him manage his sleep. What is important is that you give him the message and reassurance that he can manage his sleep on his own while you show him ways to do it.
