Adam,
Thanks so much for the quick reply. It doesn't seem to be looking for matching period numbers, only IDs. When I typed another entry into the Class Rosters with that same ID but a different period, the filter still caught it. Can the query count 2 columns (ID and Period) and look for where Col1>1 and Col2>1?
Another follow up question: Some classes can be offered in two periods, say 3rd and 7th. Could the Filter and query look for both of those?
Thanks again!
Ben