counting query

I have a table definition such as:

CREATE TABLE attendance
(
attendanceid serial primary key,
entered date DEFAULT current_date NOT NULL,
absent boolean,
authorization text default 'N',
timeperiod char(2) check(timeperiod in('AM','PM')),
days varchar(10),
studentid int,
unique(entered,timeperiod,studentid)
)

Which is used to record school attendance data. I am now trying to write
a query to identify trends in absences by counting the days column and
returning any student that has repeated absences on certain days. I am
struggling to return anything that does not need further manipulation in
Python before being useful.
Does anyone have any ideas?