Button from a child table to go to the parent table.

Can you confirm if you have a [Related Guardian] field? It seems you have the wrong [Related..] field in your url. The button looks correct - but I would expect to see something like [Related Guardian] instead of student since that would be the RID of the Guardian that you're attempting to get to.

Something more like this is what I would be expecting

URLRoot()&"db/" &[_DBID_GUARDIANS] &"?a=dr&rid=" & [Related Guardian]