It should work. I’ve just tested it with the script bellow. Do you have the problem when you run the select statement from a SSMS window or do you have it inside a procedure? Could it be that you have execute as statement somewhere in the code?

--Creating a demo database and a demo login

create database Demo

go

create login Demo1 with password = '1qaz@WSX3edc'

go

--Creating a schema and 2 tables on on the new schema and one in the dbo schema

use Demo

go

create schema test

go

create table dbo.tbl (i int)

go

create table test.tbl2 (i int)

go

--Creating a user without specifying his default schema

--which makes the dbo his default schema

create user Demo1 from login Demo1

go

exec sp_addrolemember db_datareader, Demo1

go

--Executing a query as user Demo1. Since I didn't

--specify the schema's name, the server will

--use the default schema

execute as user = 'Demo1'

select * from tbl

revert

go

--Modifying the user's default schema.

alter user Demo1 with default_schema = test

--This time the schema test will be used

execute as user = 'Demo1'

select * from tbl2

revert

go

--cleanup

use master

go

drop database Demo

go

drop login Demo1

Adi