Self-regulation describes how individuals assess and adapt to demands within and across environments. Research accumulated over the past quarter century identifies self-regulation as a powerful predictor of children's school success. However, studying young children's self-regulation in school is challenging. Tools that are easy and efficient to administer, closely linked to curriculum and learning in classrooms, and that do not require self-reports from children are needed. Here we report on the development and validation of the Self-Regulation In School Inventory (SRISI), a teacher-report tool designed to assess typically developing young children's self-regulation in school. Then, we present data from the SRISI that shows how different targets of self-regulation in school were related to one another, school adjustment, child gender, and achievement. Data were gathered from 28 teachers who provided ratings of 307 kindergarten children's (age range = 4.96-6.61 years old) self-regulation using the SRISI. An exploratory factor analysis on the SRISI items distinguished three targets of self-regulation in school: 'Emotion Regulation', 'Self-Regulation of/for Learning' and 'Socially Responsible Self-Regulation'. Path analysis confirmed the relationship between child gender and ER and SRSR, and between SRL and achievement. Findings are situated within a larger discussion concerning the assessment of young children's self-regulation in school.