When you create a new AD group login in SQL Server and then create the Database user based of that login it is not possible to assign it a Default Schema. If you try to assign it a default login you get the following error:
TITLE: Microsoft SQL Server Management Studio
Create failed for User ‘Test’. (Microsoft.SqlServer.Smo)
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An exception occurred while executing a Transact-SQL statement or batch. (Microsoft.SqlServer.ConnectionInfo)
The DEFAULT_SCHEMA clause cannot be used with a Windows group or with principals mapped to certificates or asymmetric keys. (Microsoft SQL Server, Error: 15259)
There is a Microsoft Connect article over it: https://connect.microsoft.com/SQLServer/feedback/ViewFeedback.aspx?FeedbackID=328585
What I had asked the people to do is qualify their object names with schema where it needs to be; even for dbo schema.
That’s the only workable work-around I had for them; other was create a login for each individual developer. Decided not to go that route because of number of users and turn around on the developer staff.