Mensa for Kids Excellence Reading Resources: https://www.mensaforkids.org/achieve/excellence-in-reading/ The Mensa Foundation recognizes and encourages education, gifted youth, and lifelong learning through resources like the Mensa for Kids website and other programs for youth and those who support them. This program is open internationally to any and all readers under 18 years of age, their teachers, and librarians.
At home ideas and activities for motivated advanced readers (and more!) https://www.scholastic.com/parents/kids-activities-and-printables/activities-for-kids/ideas-resources-motivated-or-gifted-learners-8-10.html
Suggested reading list for advanced readers: https://docs.google.com/document/d/1FtE3s7GqMi5_WVeoxz0mJXwAX79NGhw3nJ0OQS9fTfk/edit
Newsela: Newsela has a large amount of news articles for students as young as second grade. You will need to make an account but then you may search by age level and topic. Students I have worked with really seem to enjoy this! https://newsela.com/
Reading Challenges Resource from Gifted Guru: https://www.giftedguru.com/reading-challenges/
4th Grade Advanced Readers: https://www.greatschools.org/gk/book-lists/books-to-challenge-gifted-readers-4th-graders/
Other Great Reading Apps for the Summer (and beyond):
Epic: Your kiddo should already have an account for epic where he or she can find tons of leveled books from all genres. https://www.getepic.com/
Lion Overdrive - DPS's digital library: https://lion.dpsk12.org/
Swigert International Library Resources: https://sites.google.com/dpsk12.net/swigert-school-library/home
Raz Kids - this site has tons of leveled books for a small monthly fee: https://www.raz-kids.com/