The vast range of technologies available to mathematics students and teachers often makes discussions of relative benefits and pitfalls of technology use in mathematics education difficult to navigate. In this presentation, we will make a careful distinction between "conveyance" technologies and "mathematical action" technologies and draw attention to two different lenses that shape discussion of mathematical action technologies. We’ll propose some principles that can serve not only as design principles for creating technology-based learning environments, but also guide teachers in effective selection and usage of existing options. These principles include attention to constructs of mathematical and cognitive fidelity, as well as a strict adherence to making interactions between student and the scenarios mathematically meaningful. We will also consider some interesting implications for online digital assessments.