Alternatives to relying solely on student evaluations of teaching to help administrators more accurately assess teaching effectiveness
I am a recent part-time faculty at community college level. In our campus students as well as peers evaluate faculty teaching. 
We have only one student/peer evaluation per year. In my case, I got feedback from a professor who taught that course for more than 25 years. His recommendations were not that different from what student's suggested in their evaluation.  

Another option would be to test students understanding by assessing Student Learning Objectives (SLOs). For example, I give my class a questionnaire assessing their knowledge in SLOs on the very first day of the class and plans to give the same SLO questionnaire at the end of the course.    

Hope this helps!