Mind Full of Math?
Maine Mathematics Science and Engineering Talent Search site:
http://www.mmsets.org/
Mathematical Olympiads:
http://www.moems.org/sample_files/SampleM.pdf
NRICH enriching mathmatics:
https://nrich.maths.org/primary-upper
This site has MANY activities and information links
For free and helpful practice...there's always Khan Academy! Sign up link:
https://www.khanacademy.org/math
Common Core Mathematics Flow Chart:
https://jeffbaumes.github.io/standards/#
Harrington Math - lots of math games to play:
http://harringtonmath.com/game-directions/