Math:
coolmath.com
studyjams.com
http://www.commoncoresheets.com
dreambox
https://sites.google.com/wcpss.net/k-12mathematics/elementary-math-courses/4th-grade
General:
discoveryeducation.com
https://www.scholastic.com/parents/kids-activities-and-printables/activities-for-kids.html
99math.com
Reading:
Epic
Readtheory.org