Supporting students to build robust fraction schemes and operations is an enduring challenge in mathematics education. Recent research has explored a developmental trajectory of fractions schemes and operations constructed by upper-elementary and middle school students in an effort to support student learning. This study broadened the existing research by investigating PreK-8 preservice teachers' construction of fractions schemes and operations. This paper specifically explores data from PreK-8 preservice teachers regarding one scheme (Iterative Fraction Scheme) and way of operating (Three Level Units Coordination). Results focus on 13 special cases that disagreed with current conceptions of the developmental trajectory. [For the complete proceedings, see ED583989.]