Teacher Tenure?

Like many parents with children in the Evanston school systems, I have met many excellent teachers. However, I was also privy to many conversations with other parents about teachers to avoid and indeed, met teachers I felt should've retired or sought another career.
The subject of teacher tenure has been raised by J.B. Rees and nationally has been a Republican issue. I support labor in general, but I feel somewhat conflicted about tenure's local impact upon my children.
What are other Evanstonians opinions about this issue?