Does Tenure Protect Bad Teachers or Good Schools?

From today’s NYT “Room for Debate”:

Teacher tenure laws deprive public school students of their right to an education by making it difficult to remove bad teachers, a California judge ruled on Tuesday. The case, Vergara v. California, pressed by parents backed by a Silicon Valley millionaire, David Welch, is expected to be the first of many around the country to take on tenure.

Do tenure’s job protections prevent bad teachers from being fired or do they provide for greater stability for low-paid faculty?

Read several viewpoints in this debate here.