Almost all charter schools employ on an at-will basis. It's very important to make sure their verbal or written agreements don't change that at-will status. A charter school should never put anything in writing that would suggest an employee remediation plan or a satisfactory teacher evaluation indicates continued employment. It's good practice to clearly explain at-will employment in any teacher or administrator contract; in fact, it's good to have the employee specifically initial that paragraph. Teacher evaluation policies should clearly state nothing in the evaluation changes the at-will nature of employment.
I've found that because at-will employment is so foreign to school district personnel or legal counsel, that it's best not to get employment advice from them. However, good legal counsel will ensure charter school documents, such as the employee handbook and board policies, are in good shape should the charter school have to dismiss an employee. The only reason to use employee contracts is to stipulate the expected hours or days the employee should work and the related salary. Contracts should never include language that suggests a term of employment.
Another aspect folks have a hard time breaking out of the public education mold for, are step and level salary schedules. Some charter schools refuse to use a salary schedule and instead employ on an individual, negotiated basis. Many other charter schools effectively use performance pay systems. (Click here to read a Lexington Institute report, which includes the model in use at Liberty Common School.)