My 8 year old did elementary rote math with kumon series upto prealgebra1 along with mathantics, khan academy and whyu.org.
Nowadays, schoolyourself.org and whyu.org seems to start clicking for him. AOPS hard problem is hard.. he gets rustrated at this age and not dealing frustraction very well.
So we are doing singapore intensive practice instead from 3A and that seems working fine. Anyway, I definietly recommend whyu.org, schoolyourself.org and aops video section for ealry algebra introduction.