We learn that Atticus is a very intelligent man who is well aware and is a good role model for his children.

‘But I never figured out how Atticus knew I was listening, and it was not until many years later that I realised he wanted me to heat every word he said’

I think this because Atticus wanted Scout to hear every word he said but he did not say what he wanted directly to her but spoke to Uncle Jack. I think that speaking about someone ‘behind their backs’ with them actually present makes them truly know that that is what other people are thinking about them. If Atticus just told this straight to Scout ,face to face, she’ll feel as though she should rebel against her fathers word to get her way. If this were to happen, it would go against Atticus’ intentions.