4.813.3 Experience shall mean months, days and years of certificated employment in the Ann Arbor Public Schools. If two or more teachers have the same seniority and the Board must decide on laying off one of the teachers, the last four digits of the teachers social security number will be used as a tie breaker. The lower number will have the most seniority.

Source: Sara Mead’s Policy Notebook at EdWeek. She continues,

On LIFO more generally, the point isn’t (or at least shouldn’t be) that seniority has no place in layoff decisions. Lots of employers take seniority account, along with other factors, in making all sorts of personnel decisions, for perfectly good reasons, and it would be dumb to prohibit schools from doing so altogether. The issue is whether seniority should be the FIRST and in many cases ONLY factor in these decisions. Neither extreme–mandating consideration of seniority on its own, or banning consideration of seniority at all–is optimal; something more in the middle would be better, but that requires policy change.