There's two hurdles for the pre-algebra student: numbers being generically represented as letters and the idea of axioms being generic rules for numbers. Check

There's two hurdles for the pre-algebra student: numbers being generically represented as letters and the idea of axioms being generic rules for numbers. Check to see which issue or both is misunderstood. If it's numbers as letters, show them any interactive programming environment and demonstrate the idea of letters as generic numbers. From there, axioms are just more interactive demonstration.