While packing away some printed materials, I came across a 'hard copy' of this story and re-read it pretty carefully, thinking of the debate it had engendered on 'reality vs. fantasy' (RE children's reactions to disciplinary spanking).
Anyway, there was no overt indication that Josh felt any erotic arousal upon being paddled by Melissa, although I'd figure that he still might have. However, the boy did believe that he was gradually turning into a disrespectful brat due to his mother's ineffectiveness in disciplining him (without using CP)--while he didn't like that he was being disobedient to her and thereby making home life harder for her, Josh lacked the personal self-control to stop himself from exploiting his mother's weakness. He apparently thought, as an eleven-year-old, that taking advantage of opportunities to misbehave, at least when there would be no serious consequences, was expected of any boy who wasn't a 'goody-two-shoes' type.
So he'd wanted to be given a degree of strict external discipline, to help make himself into a 'better person' who wouldn't cause problems for his mother, and he was able to take advantage of Melissa's willingness to spank him very soundly to accomplish that. (It's certainly possible that she sensed the boy's emotional need to be punished for his misconduct, although he certainly underwent much more corporal correction from her than he'd originally anticipated.)
When his mother, influenced by Melissa's report that her supposedly administering a single solid butt-whacking had made Josh obedient and cooperative for a full week, started to corporally chastise him herself, he was gratified that his tendency to misbehave was being maternally controlled, and consequently he was treating his mother more respectfully (and therefore lovingly). Of course, he still was concerned over how Melissa was going to treat him during another imminent lengthy period of being his babysitter, since she clearly didn't mind thoroughly paddling his bare behind quite regularly.
Then there's the irony that Josh was walloped twice a day for initially lying to Melissa, yet of course she lied to his mother RE how many spankings she'd given him...

--C.K.