Attendance analysis for clubs works differently than for normal lesson registers because clubs do not feed into your statutory roll call marks. As such, you won't be able to report on club attendance in the same way (such as through the Students > Attendance > Statistics page). Instead, you'll need to collect your attendance data and calculate the percentage outside of Arbor.
First, make sure the club has been set up to take attendance, and that attendance marks have been input - you can see how to do this here: Taking attendance for Clubs and Trips
Next, go to the Students > Attendance > Registers by Date page to print out the registers and calculate how many students were present for that session.
Click the grey Club Session Overview button.
Click the green Download Register button to download this session attendance into a PDF.
You can then do the following calculation:
(Students Present divided by Total Students expected) x 100
In this example, 12 students attended the session, 10 were present and 2 were absent.
10 ÷ 12 = 0.833
0.833 x 100 = 83.3% of students were present for this session
You could do this for multiple sessions over a week and then calculate an average for that week.