NewsELA is a free service which offers thousands of leveled texts. Students can read and annotate digitally, and choose from typically four or five lexile levels (all clearly labeled!). Topics cross all subject areas and are easily searchable.
You can import class lists from other services, including Google Classroom, so you do not have to add the kids manually. I'd love to see that happen with Schoology as well. Additionally, it would be amazing if an article from NewsELA was an additional post option for teachers, as opposed to just posting it as a link, so student could clearly see what it is.