We present the motivation, design, and preliminary study of a mobile-enabled, blended learning technology called the Cognitive Learning Companion (CLC). The CLC concept emerged from field studies with teachers and students in Africa. These studies led to two key high-level requirements that shaped the design philosophy of CLC: 1) seamless support for different modes of learning and teaching in a blended scenario (where a student learns in part through face-to-face interactions with a teacher in a classroom, and in part through a combination of teacher and system supervision/direction outside of class) and 2) support for tracking student engagement and sentiment during this blended learning journey, and the interplay of these affective processes with concept and skill-building processes as part of learning. In this paper, we discuss findings from the field studies and outline our approach to address the requirements. We present the overall architecture and design of CLC. The first version supporting a core set of capabilities for blended learning has been implemented as mobile applications for teachers and students. We conducted a limited pilot to test the technology in an actual classroom setting. We also report on a usability study of CLC that demonstrates user awareness and support for data-driven cognitive decision-making in education.