Much depends on how you data is structured. The type of chart you want also is important to know.
If you have a table where each record records whether a student did or did not attend on a given day, you can use a layout based on that table to count the number of students that did or did not attend on each day by sorting your records to group them by date and charting summary fields to get your y axis series of values.
I understand now, i've solved it.
it really simple, i just have to study more about chart and summary.
thank you so much for your answer, it help me a lot.