Expanded learning time (ELT) is a practice that entails increasing the length of the school day for all students, with the goal of improving student outcomes, especially in low-performing schools. Boston Public Schools (BPS) has been implementing ELT as an improvement strategy in low-performing schools since 2006. In 2015 the district drastically increased the number of participating schools, with a plan of expanding the day in 60 elementary, middle, and K-8 schools by 2018. How much additional time is added to the school day and parameters for using the extra time depend on the ELT funding source, but, in general, schools have wide latitude for program implementation. BPS collaborated with American Institutes for Research (AIR) on IES-funded grant R305H150013 to study its ELT program types, with the goal of understanding the impact of ELT on student academic and behavioral outcomes. Staff from both BPS and AIR collected data, using extant data and interviews to determine the amount of time added to each school's day, how the additional time is used, and the perceived strengths of ELT and challenges encountered by staff when planning for and implementing it. This report describes the results from the first year of the study, which sought to identify common uses of time in the 46 schools implementing ELT in school year 2015-16 as well as perceived strengths and common challenges. Overall findings from the study reveal the following: The district lacks centralized information about schools' time usage, a potential barrier to understanding ELT implementation. The amount of time added varies by ELT policy and funding type, with no single districtwide system. Allocation of time also varies, with some relationship to instructional focus. The greatest reported strength of ELT--teacher satisfaction about its potential for student outcomes--is at odds with the greatest reported challenges--lack of teacher buy-in and teacher burnout. In the next stage of research, AIR and BPS will collaborate to design and implement small-scale impact and cost-effectiveness analyses based on the findings about ELT described in this report. Of particular importance are considerations for how ELT is used in different BPS schools--considering not just how much extra time students receive but also what they do with that time. Another important consideration is schools' instructional foci and goals for ELT in relation to student outcomes.