I have used and loved the iDoceo app for many years. I originally purchased it when it was free, now it is only $17.99 (AU) but it is well worth your money. There is no need for a diary, everything you need is embedded within the app. I have used it for both primary and secondary classes. I love fact that you can easily export your diary/grades etc as PDF or EXCEL documents. Also, it is great for managing multiple classes and collating data for reporting.