Reading:
https://www.raz-kids.com/
https://www.scholastic.com/teachers/bookwizard/
Spelling:
http://www.spellingcity.com/ncasciola/
Math:
https://xtramath.org/#/home/index
www.coolmath4kids.com
www.math-play.com
www.funbrain.com
Science
https://spaceplace.nasa.gov/
https://pbskids.org/designsquad/