This paper addresses a wicked problem faced by leaders wanting to be evidence informed in their choices of school improvement priorities and the most productive leadership practices to enact in pursuing those priorities. While local contexts will always be central to these choices, results of research ought to provide useful points of departure. But determining what relevant evidence recommends, local context aside, is far more difficult that the admonition to be "evidence informed" seems to imply and the research community has offered few systematic solutions to the problem. This paper offers one possible solution, the calculation of "Power Indices" using, for the purposes of illustration, evidence about the effects of a selected set of potential school improvement priorities (teachers' emotions) on student learning, in combination with evidence about the effects on teacher emotions of a selected set of transformational leadership practices. Results argue for the value of a unique line of future research enabling school leaders to make choices about both school improvement priorities and how they might best pursue those priorities that systematically reflect the results of relevant evidence.