This report describes research carried out at in an EFL public speaking course at a Japanese university. While student presentations typically involve both delivery and student slideshows being assessed at the same time, this investigation looks at separating the two components and assessing presentation slideshows separately. Using a summative assessment instrument, a slideshow rubric, a series of related formative assessments were also developed and administered with the goal of creating an synergy of assessments whereby the combined effect of interweaving these assessments together would promote greater student learning. The 22 university students in this class engaged in trio of related assessments (two formative, one summative) in developing a slideshow for a persuasive speech. Students produced a first draft of their presentation slideshows, and these were used for a self-assessment, and also for a formative teacher assessment (ungraded) prior to the final graded summative assessment. The report into the formative use of summative assessment describes the processes and instruments used in this experiment in assessment synergy. Assessment information and data from five students in the class provide actual assessment examples to help delineate the processes described. These student examples, and the teacher feedback included, help demonstrate that the formative use of summative assessment had positive effects on student learning related to the effective construction of presentation slideshows. The report concludes with a call for more classroom based research and publications in EFL/ESL contexts related to the synergy of formative and summative assessment processes, practices and instruments.