Zach is the eldest of the two Florrick children. He is seen as the 'good' child in the family with his excellent grades and avoids trouble with his parents, Alicia and Peter Florrick.
When photos of Peter smoking pot and of his infidelity is left at their apartment's doorstep, he opts to not tell Alicia about it, knowing that it was sent to her to hurt her. After some digging, he realizes that the photos were in fact photoshopped. When Peter later comes home on house arrest, he shows them to Peter.
At one point, Zach begins to see Becca, a junior from his high school, who tries to make him rebel, particularly by giving him an Islamic CD which she told him to play whenever his parents are giving him trouble.
It is revealed in Fleas (and Silly Season) that Zach had a pack of condoms that Alicia hid in her drawer after she had 'the talk' with him. When Peter later discovers it, Alicia took them with her to spite Peter. When Zach later finds it missing from her drawer, he continues to go off with Becca, who had just told him that she is sure about having sex with him.
Zach breaks up with Becca when he finds out that it was her who was tweeting about Alicia.
Nisa was the girlfriend of Zach. It is discovered on season 6 episode 4 that Nisa was pregnant with Zach's baby but chose to get an abortion instead. It is also seen in a flashback that their relationship was very secretive from Alicia, who was unaware of the pregnancy and the abortion which Zach was present for until she started running for State's Attorney.