From a paper by Brian A. Jacob Journal of Labor Economics Vol. 31, No. 4 (October 2013), pp. 727-761. The title is "The Effect of Employment Protection on Teacher Effort."
In 2004, the Chicago Public Schools and the Chicago Teachers Union signed a new collective bargaining agreement that gave principals the flexibility to dismiss probationary teachers (those with fewer than 5 years of experience) for any reason and without the hearing process typical in many urban districts. Results suggest that the policy reduced annual teacher absences by roughly 10% and reduced the incidence of frequent absences by 25%. The majority of the effect was due to changes in the composition of teachers in the district, although there is evidence of modest incentive effects for young untenured teachers.A draft (2012) is here.
In the past, it has been extremely difficult for principals to dismiss teachers outside the auspices of a RIF. Like most other districts, the collective bargaining agreement in Chicago provides considerable protection for tenured teachers that make it very time-consuming and difficult for principals to dismiss these teachers for cause. Unlike many smaller, suburban districts in Illinois, however, the collective bargaining agreement in Chicago also made it very difficult for principals to dismiss non-tenured teachers. (Page 8 in the draft).