We can't see your file and so can only give general directions.
Make sure that you know in what table is defined your District Name field that populates with a name when you enter a school name. Open Manage | Database | Fields, find this field's definition and double click it to open Field Options. Click on the Auto-enter tab and check for ether an auto-entered calculation or a looked up value setting. Either option will give you the name of a table occurrence that's the starting point for the auto-enter feature and a table occurrence from which the data is looked up. A "table occurrence" is a 'box' on the relationships graph so with those two names, you should be able to spot the relationship used in your relationships graph. You can also replicate the settings you find here in other fields to do the same type of look up.
Other possible ways this might happen:
- Your Auto-Enter option might be a calculation using ExecuteSQL to copy over the needed data. In which case, there's no relationship used to look up the data beyond any "join clause" that might be used in the actual SQL query.
- A script trigger might be tripped when you edit the school name field. The script performed by the trigger may find the needed data and set the district field to a value. If this is the case, you can right click the School Name field and select script triggers to see a list of script triggers set on that field. From there, you can identify and edit this script to set other fields to data just as it now does with the district name.