The Center for American Progress has analyzed the law in all 50 states and concludes:
Districts recognize that an inability to dismiss poor-performing teachers undermines efforts to ensure that every student is taught by a highly effective instructor. As districts begin implementing more effective evaluation systems that better identify both low- and high-performing teachers, changes will have to be made to dismissal processes to exit those teachers in a fair and efficient manner.
Go the main link and you'll see a 50-state analysis. Arkansas, though its law provides for dismissal of incompetent teachers, is criticized for not providing clear definitions and procedures for removal of inadequate teachers.