Timely and credible data on student learning has become a global issue in the ongoing effort to improve educational outcomes. With the potential to serve as a powerful diagnostic tool to gauge the overall health and well-being of an educational system, educational assessments have received increasing attention among specialists and the media. Though the stakes are high, relatively little is known about the cost-benefit ratio of various assessments compared to other educational expenditures. This paper presents an overview of four major types of assessments--national, regional, international and hybrid--and the costs that each has incurred within 13 distinct contexts, especially in low-income countries. The findings highlight broad variation in the total cost of assessment and the cost-per-learner. This underscores the importance of implementation strategies that appropriately consider scale, timeliness, and cost-efficiency as critical considerations for any assessment. (Contains 15 notes and 2 tables.)