Main Ideas / supporting details online practice: 

https://www.wgtn.ac.nz/llc/llc_resources/academic-writing/tsent1.html

Link to site

https://www.ixl.com/ela/main-idea

Click here to practice: find the main idea and the supporting details. 

Online Quiz Exercise 

Find the main idea - a quiz

https://sites.google.com/view/ironiydreadcomp/find-the-main-idea

Miri Osherov - Main Idea activity

https://www.speechandlanguagekids.com/helping-children-to-identify-main-ideas-and-supporting-details-when-reading/