Estimation of task size is important, especially in an Agile world where the exact specification of a delivered unit of work may not even be apparent when attempting to schedule work. Where technologies and the environment in which they are to be used are well understood existing models can be used – but what of new technologies, or new environments? Raw estimation is the starting point – an expert group convenes and uses a method such as “T-shirt sizing” to decide if a particular piece of work is “small, medium, large, extra-large” – or some other comparative estimate of the time and effort required to deliver. Such a model can only be an effective planning tool if it’s cross checked against actual effort: do the people making the estimates have enough information on hand to accurately estimate in the first place? Part of the wrap-up stage of any piece of work has to be the comparison of actual effort against estimated effort to make sure future estimates are suitable for planning. If the initial estimate as accurate enough, then great – the estimating model works, so keep using it. If, however, the inital estimate wasn’t accurate then corrective action needs to be taken. The leadership team on the project needs to investigate to understand what caused the work to overrun the estimate. In some cases, an external factor will be identified as a once off cause – perhaps a key staff member wasn’t available or a supplier had a delivery problem. In other cases, it raises a red flag because if the estimates are not accurate there will be a knock on effect on the rest of the work schedule. Validation requires honesty, courage and wisdom: the honesty to accept and understand that early estimates may not be accurate the courage to review in the face of a human desire not to be shown to have “failed” the wisdom to understand that estimate review and validation isn’t about apportioning blame or finding mistakes, but is in fact a very effective tool for improving project efficiency and performance. So – are you using honesty, courage and wisdom in your project estimation validation?