You could use the restricted user group gpo setting
computer configuration \ windows settings \ restricted groups
group = your group to be made local admins
member of = BUILTIN\Administrators
There is absolutely nothing that has to be done on the client side.
Create the gpo in the ou where the Computers reside (NOT the users), go to
computer configuration/windows settings/security settings/restricted groups,
right click on restricted groups and select new group (For the local
computers, this group name should be - administrators) and key in the group
you want auto populated. Select add on the Members of this group and then
add the members you want populated.
MVP - Directory Services
MCT, MCSE, MCSA, Security+, BS CSci
2003, 2000 (Early Achiever), NT
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