Willis and Arnold had this real GRUNGY look in season one. Their hair was never combed or brushed, their clothes were ran down looking. They just looked a mess in season one. But they looked a %100 better in season 2. They no longer had the GRUNGY Look.

The fashion in DS has always been quite funny, considering how rich Drummond was- his clothes always looked cheap. I remember in a season 3 episode he was wearing a bright yellow jumper that looked ridiculous!

your right, that didn't make much sense.

Maybe they wanted to be sure that the audience would not forget that the boys were from a poor neighborhood in Harlem. Willis was forever reminding us of that in the first year.

It was probably just a matter of comfort. If I was suddenly taken out of my environment, and put into an environment that was totally foreign to me, I'd probably try to hang onto what was familiar as well. Wearing those clothes was probably just a way for them to hang onto their past.