Maybe this is a bit tentative, and I'm certainly not a parent myself, but:

Sometimes, having an authority figure tell you what to do can be status-lowering, even when the authority figure in question is trying to give you useful advice, or force you to do something which benefits yourself. Would it be possible to preface future conversations where you need to steer Alex in a different direction with a few statements that build up his self esteem, and end the conversation by praising him for doing a good job on something or other?

I'm an adult, and this sort of thing works on me, too.