In this short video segment, assessment giant W. James Popham gives a brief but thoughtful description of formative and summative assessments and how they differ. This might be a helpful resource in training teachers on the purpose and value of formative assessment (forgive the cheesy music intro...):
Popham describes the research base supporting formative assessment, and notes that, "whereas formative assessment intends to improve on-going instruction, summative assessment tries to answer the question, 'Was instruction effective?'"
I find that, as much as teachers are talking about formative assessment in recent years, there's still a lack of real understanding about these differences.
Popham also notes that, while most statewide standardized accountability tests are considered "summative," most are not particularly good at measuring the real impact of teaching on student learning (what he calls a tests "instructional sensitivity;" for more on this see the final chapter of Popham's book Transformative Assessment). For this reason, well-designed and implemented formative assessment techniques are one of the best tools for measuring the actual impact teachers are making on student performance. School leaders should take this into serious consideration, not only for supporting meaningful classroom-level assessment, but also in evaluating teacher performance.