clotfelte ladd vigdor arrived to this conclusion through the estimation of a model with student fixed effects that minimizes possible bias using data from north virgina at the high school level after ruling out alternative explanations like prior achievements or sociocultural environment they find a positive relationship between teachers college ratings and test scores as well as a positive relationship between teachers degrees coursework and certification and student outcomes in mathematics good grouws ebmeier were among the first analytical study of the links between teachers education and in particular inservice education and student performance this study wanted to put into evidence the impact on students of their mathematics teachers continuing training to do so teachers were assigned randomly to either a control or a treatment group