This is a tricky question as it covers a wide scope, and additionally it is biased by the teachers personal judgement of a technology. For example, if a teacher argues for funding for iPads, when these iPads arrive he/she will favor those iPads as an educational tool no matter what because of the effort he/she put into getting them. In a similar manner a teacher may hold a negative view of a technology and therefore see educational deficits.
Therefore, an objective measure of ICT success is required – the question is, what? I think the most basic thing is is measuring success on a learning objective before the ICT is applied, and after – therefore testing the objective or the time in which an outcome is learnt before – with and without the particular ICT. Running record, observation, etc.