ITT (“intent-to-treat”) represents the​ ​impact for all students who were assigned to STARI, regardless of the amount of curriculum they completed. But the amount of the program students actually covered mattered.​ ​TOT (“treatment-on-the-treated”) represents the​ ​impact​ ​when controlling for engagement with the program, as measured by the percent of workbook pages on which students had done any work.