SQL query slow with call to function

Question

I have a SQL query that will return in less than a second or two with a function in-line selected in the "from" clause of the statement. As soon as I select that returned value in the SQL statement, the statement takes from anywhere from 2 to 5 minutes to return. Here is a simplified sample from the statement:
This statement returns in a second or 2.
select A.pk_id
from stu_schedule A, stu_school B, stu_year C, school_year D,
(select calc_ytd_class_abs2(Z.PK_ID,'U') ytd_unx
from stu_schedule Z) II
where B.pk_id = A.fk_stu_school
and C.pk_id = B.fk_stu_year
and D.pk_id = C.year
and D.school_year = '2011';
if I add this function call in, the statement runs extremely poor.
select A.pk_id,
II.ytd_unx
from stu_schedule A, stu_school B, stu_year C, school_year D,
(select calc_ytd_class_abs2(Z.PK_ID,'U') ytd_unx
from stu_schedule Z) II
where B.pk_id = A.fk_stu_school
and C.pk_id = B.fk_stu_year
and D.pk_id = C.year
and D.school_year = '2011';
Here is the function that is called:
create or replace FUNCTION calc_ytd_class_abs2 (p_fk_stu_schedule in varchar2,
p_legality in varchar2) return number IS
l_days_absent number := 0;
CURSOR get_class_abs IS
select (select nvl(max(D.days_absent),'0')
from cut_code D
where D.pk_id = C.fk_cut_code
and (D.legality = p_legality
or p_legality = '%')) days_absent
from stu_schedule_detail B, stu_class_attendance C
where B.fk_stu_schedule = p_fk_stu_schedule
and C.fk_stu_schedule_detail = B.pk_id;
BEGIN
FOR x in get_class_abs LOOP
l_days_absent := l_days_absent + x.days_absent;
END LOOP;
return (l_days_absent);
END calc_ytd_class_abs2;

Answer 1

Query returns anywhere from 6000 to 32000 rows. For each of those rows a parameter is passed in to 4 different functions to get ytd totals. When I call the functions in the in-line view but do not select from them in the main SQL, the report (oh, this is Application Express 4.0 interactive reports, just an FYI) runs fast. The report comes back in a few seconds. But when I select from the in-line view to display those ytd totals, the report runs extremely slow. I know there are the articles about context switching and how mixing SQL with PL/SQL performs poorly. So I tried a pipeline table function where the function for the ytd totals populate the columns of the pipeline table and I select from the pipeline table in the SQL query in the interactive report. That seemed to perform a little worse from what I can tell.
Thanks for any help you can offer.