Can I view a child's reading over time?

Yes you can view a child's reading over time. 

You can change the date range on the Teacher Dashboard to an earlier date. This will show you reading that has taken place since then and the subsequent 7 days. 

There's also a this week and a last week date range. When you log out it'll remember the date range that you last selected. 

At the moment, there's no way to view this over longer spells of time.