I have a script A which calls a script B.
Script A has a variable $var.  Script B assigns a value to variable $var.

When script B finishes, and I get the value of $var in script A, the value remains unchanged (original value, not what B set it as.)

It's as if B changes a copy of $var, not the original $var that was in A.  I need changes that script B makes to $var to stay.

I tried defining $var as global in A, Set-Variable var -scope global.

But the same thing happens. 

Thanks for your help!

Can you show us your scripts? Make sure you the proper syntax both when reading and stiing the variable. A shortcut is to simply use the syntax $global:var.