The study examined whether embedding the linear equations and ratio and proportion strategies used to solve percent problems in the higher-order structures of proportional logic and group properties would aid achievement. Thus, it examined the interaction in differences in understanding fundamental structures in mathematics, and instruction requiring their use in solving percent problems. Participating were 141 eighth-grade students aged 12-14 from six intact classes. Three 10-item tests were constructed to assess achievement in solving percent problems; understanding of proportionality and group properties was clinically assessed with a balance beam task and a figure rotations task. Two sets of parallel units were prepared, one based on ratio and proportion concepts and the other on the solutions to linear equations. It was found that the attainment of formal operations for proportional logic was not associated with short-term success for solving percent problems with the ratio and proportion method, but it was for the delayed posttest 6 weeks later. For the linear equation method, both short- and long-term success required understanding of the structures for both group properties and proportional logic. Other results are also reported and discussed. (MNS)