This paper presents research conducted as part of the field test of the University of Chicago School Mathematics Project's (UCSMP) curriculum, Fifth Grade Everyday Mathematics. The UCSMP curriculum is one of the current reform programs funded by the National Science Foundation to implement the Standards of the National Council of Teachers of Mathematics. In this study a timed mental computation test was given to (n=78) fifth-grade students who had been in the UCSMP curriculum since kindergarten. The UCSMP students outperformed the baseline group on all but one of the 25 items. During interviews UCSMP students rarely used a mental version of a paper-and-pencil method and tended to employ some of the methods used by good mental calculators. (MKR)