PS I love Alcumus, but I don't think doing number theory in Alcumus is going to help by leaving lots of third and fourth grade topics untouched! You do pretty much have to be able to do arithmetic to do number theory, and as Grinity (was it?) said there's not really a whole lot else in school maths at this kind of level. (There is *some*, at least in UK maths there is - but it's only going to occupy another couple of afternoons.)

Email: my username, followed by 2, at google's mail