The Math Circle is a Fall program for elementary and middle school students from Charlottesville area schools, taking place on UVa grounds. The Fall 2019 program is for 6th and 7th grade students. 

http://as.virginia.edu/ampersand/expanding-circle

References used in the 2019 program include:

"Mathematical Circle Diaries, Year 2: Complete Curriculum for Grades 6 to 8" by Anna Burago. Published by the American Mathematical Society. 

"Mathematical Circles: Russian Experience" by Dmitri Fomin, Sergey Genkin, and Ilia V. Itenberg. Published by the American Mathematical Society. 

Winning Ways for Your Mathematical Plays: Volumes 1-4, by Elwyn R. Berlekamp, John H. Conway, Richard K. Guy. Publisher: A K Peters/CRC Press.