Assessments of instructional quality based on classroom observations and artifacts have the potential to measure and improve mathematics instruction and learning. This article describes the Instructional Quality Assessment (IQA) Mathematics Toolkit and examines its ability to identify the nature and quality of classroom instruction. The IQA assesses elements of ambitious instruction in mathematics; specifically, the level of instructional tasks and task implementation, opportunities for mathematical discourse, and teachers' expectations. Results are reported from a study of 13 middle school teachers in a mid-sized urban district, following a professional development initiative and the adoption of standards-based mathematics curricula. The IQA identified high-quality assignments and student work, and that teachers who utilized cognitively challenging tasks could maintain the cognitive demands in lesson observations. The IQA also identified that observed instruction lacked high-quality whole-group discussions. The article closes by discussing how IQA can provide feedback for instructional improvement at the district level. (Contains 1 figure, 9 tables and 2 notes.)