Welcome to the forum.
Try having your button (which is entirely within the portal row) run "Go To Related Record" instead. This command lets you choose the layout you wish to use...choose your School editing layout.
Note: you can make the school name field itself (or every field in the portal row for that matter) a button instead of adding a separate button. Click on anything in that line and it will go to the related record.
I started out with the school name as the button with Get Related Records but it was not working. I did finally get a separate button to work by copying one from a template database. One other thing though, when I use this button to go to the new layout of the detail for this school, I wanted to have a checkbox that if you click it yes, it takes you to a new form/layout to enter additonal information. I get the checkbox to work but again, I cannot get it to open the affiliated form for this school or if no info is available, I would like it to open new record. Any suggestions?