The three important features you need for your school life are brought together in this app:

1. Marks Management
2. Timetable
3. Agenda

My suggestion: Since the app is free of charge and add-free, just download the app and convince yourself of the simplicity and reliability.

Nevertheless here some information about the three aforementioned main features:

In the Marks Management tab the app always shows you the current averages of all your subjects. Of course you can have a closer look at every single exam you created. To every mark you can assign a weighting a date and a note.
The app also calculates your overall average. It is designed very universal, so all sorts of grading systems should be compatible.

In the second tab you can arrange your own timetable. Due to the fact that the agenda is directly integrated into the timetable you can see immediately if for a particular lesson an exam is announced or homework has to be done.

If that is not enough, you can buy the PRO version using in-app-purchase. All sorts of features will then be unlocked. For example the averages can be displayed rounded or you can turn on notifications for exams or tests and so on..

In my book, these are enough reasons to just download School Marks Manager and convince yourself that this app is by far the best one in its category! ;-)