Recent work has demonstrated that having students study worked examples and answer self-explanation prompts as part of their problem-solving practice improves learning on researcher-developed measures of mathematical proficiency. However, little work has been done to date to investigate whether these benefits translate to improvements on the types of standardized assessments typically used by school districts to assess proficiency and make curricular decisions. In the present study, we examined the impact of using worked-example and self-explanation prompt assignments on the performance of 5th grade students in one urban district on two district-administered standardized tests: i-Ready and PARCC. Results indicate the approach effectively improves student mathematic scores on both standardized measures. This study provides policy-meaningful outcomes. The findings from the current study show that standardized assessment scores can be improved by merely changing the type of practice problems that students engage with. Interventions like this provide a pathway for underperforming schools and districts to improve student achievement through easy access points, which are low-cost and can be added to the curricula districts currently use. [This paper will be published "Journal of Research on Educational Effectiveness."]