This research brief examines the challenges and opportunities presented in evaluating whether an intervention achieves defined goals of increasing students' educational attainment, employment, and earnings after high school. The report concludes that evaluations should: (1) Distinguish between gross outcomes (such as how many young people attend college after high school) and net impacts (the extent to which these outcomes were caused by the policy or practice being studied, rather than by other factors;(2) Explore whether policies and practices have different net impacts for certain subgroups within the high school population; (3) Test policies and practices on a large scale and in a variety of real-world settings; (4) Include analyses of program implementation and cost; and (5) Acknowledge that certain policies and practices can make a significant difference for at-risk students even when the outcomes for these students do not appear favorable in an absolute sense. The report recommends that policymakers, administrators, and researchers work together to determine which interventions are most effective in preparing students for post-high school transitions. Expanded use of random assignment studies should continue, along with efforts to strengthen alternative, quasi-experimental methodologies. Net impact studies should be conducted at scale in real-world settings and be accompanied by analyses of program implementation and costs. These approaches will provide a better understanding of the prospects for widespread replication of successful efforts. Although acknowledging the challenge of conducting such evaluations, the author advocates that it can also improve high school accountability. (Contains 4 endnotes.)