This article features FAST-R, or Formative Assessments of Student Thinking in Reading, a new assessment tool that measures critical-reading skills. FAST-R was developed by the the nonprofit Boston Plan for Excellence (BPE), a local education foundation, to provide teachers with information about what students are thinking when they try to find evidence and make inferences based on texts. Those two core reading skills are a central part of the state testing program, the Massachusetts Comprehensive Assessment System, or MCAS, and vital to youngsters' ability to read for understanding. Piloted in 18 schools in the 2003-04 school year, with support from the Menlo Park, California-based William and Flora Hewlett Foundation, FAST-R is now used in more than 50 schools in the 57,000-student Boston district.