After the first Season of this show Paul's voice changed quite a bit. For the first few episodes of the second Season it was in sort of a transitional period. Like in the episode where they go to Atlantic city and Kevin meets that girl who's older than him. You can tell his voice is cracking during that one, cause in some scenes it sounds deep, and other scenes it's high pitched like it was in the previous season. The Same is true of the first day of school episode from that year with Mr. Collins. I think by the next episode tho. The one where Kevin's mother doesn't want him to play football, it has totally changed to the voice he had from then on out. Anyone else notice this? Also I think Kevin's voice gradually changed somewhere between The Lake episode and the Christmas episode of Season 4.

Like in the episode where they go to Atlantic city and Kevin meets that girl who's older than him.

Tsk, tsk, it was Ocean City.

After the first Season of this show Paul's voice changed quite a bit. For the first few episodes of the second Season it was in sort of a transitional period. Like in the episode where they go to Atlantic city and Kevin meets that girl who's older than him. You can tell his voice is cracking during that one, cause in some scenes it sounds deep, and other scenes it's high pitched like it was in the previous season. The Same is true of the first day of school episode from that year with Mr. Collins. I think by the next episode tho. The one where Kevin's mother doesn't want him to play football, it has totally changed to the voice he had from then on out. Anyone else notice this? Also I think Kevin's voice gradually changed somewhere between The Lake episode and the Christmas episode of Season 4.
I didn't think that Paul's voice changed to much until the 4th season. Kevin's voiced stayed pretty much the same until Season 5.

I don't recall any voices changing on the series, with the exception of Warren Gander in the "Glee Club" episode. (It reminded me of an episode of The Brady Bunch in which Peter's voice changed while the Bunch was recording a song! Appropriately they sang "Time To Change"!)