The introduction of technology enhanced learning (TEL) methods changes the deployment of the most important resource in the education system: teachers' and learners' time. New technology promises greater personalization and greater productivity, but without careful modeling of the effects on the use of staff time, TEL methods can easily increase cost without commensurate benefit. The paper examines different approaches to comparing the teaching time costs of TEL with traditional methods, concluding that within-institution cost-benefit modeling yields the most accurate way of understanding how teachers can use the technology to achieve the level of productivity that makes personalisation affordable. The analysis is used to generate a set of requirements for a prospective, rather than retrospective cost-benefit model. It begins with planning decisions focused on realizing the benefits of TEL, and uses these to derive the likely critical costs, hence the reversal implied by a 'benefits-oriented cost model'. One of its principal advantages is that it enables innovators to plan and understand the relationship between the expected learning benefits and the likely teaching costs
