Software engineering methods and metrics to estimate development time for the development and maintenance of computer-based training (CBT) differ from methods and metrics used to develop large information systems. The estimation techniques for large information systems employ Lines-Of-Code and Feature/Function points to calculate project effort in staff-months [Boehm 1981], techniques that are difficult to apply to CBT effort estimation. For the development of computer-based training systems, Development to Delivery Time Ratios have been the usual estimation metric, but these also have limitations [Marshall et al. 1995]. Metrics to accurately measure the development effort of Multimedia Information Systems (MIS) are currently being developed and investigated [Fletcher et al. 1997], but still differ from computer-based training systems development. This paper presents an estimation model for effort development of small courseware projects (less than 2 staff-months). By identifying the sub-tasks of the development phase, an individual estimation technique is suggested for each sub-task. The sum of all sub-tasks estimations determines the total effort estimation for the development phase of a particular lesson. Incorporating historical data as a baseline and identifying risk cost factors, this method is accurate for estimating effort of some sub-tasks and for the lesson unit as a whole. This method is not meant to be a "silver bullet" [Brooks 1995] but a start toward building an accurate estimation tool and a refinement of the development process.