Yesterday and today have been better.
Nathan reminded me that not all of Luke's screams mean the same thing. (Well, with so many, I guess they had been running together in my head :) ) Bethany also noticed that often, Luke just didn't have the words yet to say what he wanted, so he screamed. Those pieces of information were helpful to think about.
Here is my brief POA (plan of action):
Sometimes he screams when he wants something. If I ask him if he wants "x," then I can help supply the words that his screams are trying to say.
Sometimes he screams when he wants my attention. I can ignore that sometimes, or just look down and talk to him briefly and then go on with what I was doing.
Sometimes he screams because he is mad that I took something away or because another child is playing with the toy that he wants. In this case, I either take him for a brief time out, or try to distract his attention to something else.
Hopefully I will be able to tell which scream is which. :)