A bill to make it more difficult for Tennessee teachers to earn and retain tenure gained final approval Thursday in the state Senate, and Gov. Bill Haslam is expected to sign the measure into law. The bill increases the wait time for tenure to five years from three. It requires teachers to receive ratings in the top two levels of a new five-tier evaluation system in their fourth and fifth years of teaching to earn the designation. Tenured teachers ranked in the bottom two tiers also could be placed on probationary status.