The screens are looking for things like acuity and color blindness.  They are not addressing vision as a whole at all - which is what the developmental evaluation does.  These are 2 different things.  If the screens at school were performed by a D.O., then yes.  However, the screens performed here in schools and even doctor offices (and most eye places) do not screen for these particular issues.
Agreed.  I took the OP's statement of "vision assessment" to be exactly that, not a "developmental evaluation".  
The in-school vision screenings I'm familiar with are a close match with what's described by  
Prevent Blindness America - children's vision screenings. While they may not catch every problem, they've helped many students and families by flagging children who needed or would benefit from additional vision assessment.