One of the most problematic things about Season 1 was that viewers only knew what Hannah wanted them to know. As a result, it was hard for us to form opinions on characters without being influenced by what she told us. One character this relates to in particular is Zach Dempsey. The high school jock had a bit of a rough time in the first season, but it was hard to sympathise with him after he ignored Hannah's cry for help.
But unlike Bryce and the others on the baseball team, Zach is very much aware of his shortcomings, and makes a valiant effort to be better in Season 2. Helping Clay and Jessica get evidence on Bryce was a brave decision on his part, even if the whole polaroid storyline was a little contrived.
But the best part of his character development is his relationship with Alex. Following Alex's suicide attempt in the first season, Zach hangs out with him and helps him get back on his feet — quite literally, as he helps the troubled teen with his physical therapy. While the two characters did spend time together in the first season, we never got the impression that they were close to one another.
There is a camaraderie between the two in Season 2, and this relationship is certainly one of the show's highlights.