This thesis explores the use of a newly devised Subject Learning Portfolio with incorporated resources aimed at developing student self-assessment skills. In addition the study was concerned with whether the portfolio had the potential to be beneficial as a teaching and learning tool across other subject domains. The area of formative assessment is a complex area of educational theory. The Literature Review identifies how assessment definitions can diverge in terms of focus of student-controlled assessment. However the author supports the position as put forward by many in the educational arena; meaningful and truly effective assessment practise is centred in the classroom and it develops student ability to assess themselves and direct their own learning. The author embarked on a process of action research to the backdrop of preparations for the implementation of the new Junior Cycle Framework in her own school. The study found that the Subject Learning Portfolio was successful in developing self-assessment skills in the author's class group. The author recognises the critical role that the critical reflection and action process had in improving professional practice which has benefits for student learning. However the portfolio did not transfer successfully across other subject domains which highlighted universal challenges to the introduction of new resources as well as the reforming of classroom assessment practice. The research concluded that time and effective training are instrumental in effecting real assessment change. What appeared to particularly critical however is teacher engagement with critical reflection and developing innovative approaches in their own professional practice.