grant the right to select only certain rows? - Mailing list pgsql-general

If I have a table students:

name    grade_level
Joe        1
Kim        1
Lisa        2
Mike        2

And I have two database users, mary_smith and tom_white.  If Mary Smith
is the 1st grade teacher, is there any way to grant her access to only
select rows where grade_level=1?  I think GRANT only works as a
table-wide permission, but a co-worker thinks he has seen similar
behavior in Oracle, like
"GRANT SELECT AS SELECT * FROM STUDENTS WHERE grade_level = 1
ON students FOR USER mary_smith"   (Rough approximation of the type of
query I am looking for).

Thanks,
Fran