K.H.
I don't know that I can be of any help, but here's how it's been for me and my two kiddos.
Screaming from my two kiddos is *always* an attention getting thing. And actually I'd rather screaming than biting, hitting, etc. When dd was younger, and ds (1yr) now - they scream to get attention. And I decided that was okay (to a certain age). DD hasn't screamed in ages so I have no horror stories of it going on when they're old enough to know how to more effectively communicate.
That to say, your ds is only 2yrs old. He does not have the verbal communication skills to tell you what he wants to tell you. Instead he's using is vocal skills :-) The attitudes and activities that you pay attention to, you'll get more of. Perhaps this is his way of protesting being left at MDO?
At home, anyway, screaming doesn't hurt anyone. Considering the other alternatives for expression, it's among the safest :-) When dd was upset about something she used to scream and throw things. I am alright with the screaming. DH and my rules on anger expression basically say 'Don't hurt yourself, others or any property." I discourage hitting anything (like a pillow) b/c eventually it might not be a pillow. I want her to learn to express without lashing out physically. Screaming can achieve this when they're 2yrs old. For mine, just being held seems to help tremendously. I ended up grocery shopping with dd in a ring sling and then Ergo carrier. DS is still in the Ergo for grocery trips. DD was very wary of strangers and would hide her face in my chest until she felt safe enough to peek out again.
Sorry that I rambled, but I hope something that I wrote will help!
K. H, mama to
Catherine, 4yrs
Samuel, 1yr