Microsoft Teams has Assignments app in Office 365 for Education License

If you have Office 365 Education License you can get Assignments Tab/app for creating assignments for your class.

I f you don’t have Office 365 for Education, you can get it for free for your faculty and students with a valid school email address.

To signup for Office 365 for education if you are in Faculty or School https://www.microsoft.com/en-us/education/products/office/default.aspx

Microsoft has also just released several updates to Assignments functionality:

• Easy to assign engaging learning activities
• Add assignment resources from any team 
• See what your students see
• Add Close dates to your assignments 

More about it can be found here