The visit needs to be prebooked by phone dialing 0039 049 2010020 or in their Cappella degli Scrovegni On line booking system, they will give you the time you are supposed to be there and you can plan the rest of your visit according to this time. The afternoon seems to be a bit less busy as school visit are normally during morning.
Before entering the Chapel you will see a video that will explain the main facts. The video seems to be available only in Italian. I suggest you read about the Chapel BEFORE coming in, as the visit is limited to only 15-20 minutes.
The ticket you purchase includes the possibility to visit the Padova museum and Palazzo Zuckerman, if you have the spare time they are both worth a visit.I have seen the Chapel two times, first before and than after the renewal work they did in 2001. The difference is awesome, the Giotto paintings are simply incredible. The only negative thing is the short time they will give you to see.. it is not enough to see everything well.

