Organizing the twenty-eighth edition of PME-NA has been an honor, a responsibility and also a great pleasure. The vast panorama of excellent academic work that will be displayed at the conference and that is contained in these pages makes us immensely proud to be part of the project.

The Mérida Conference proposed the theme Focus on learners, focus on teachers, which comprises an extensive amount of possibilities in the juxtaposition of both ways of focusing mathematics education: Focus on learners and focus on teachers, Focus on learners or focus on teachers, Focus on learners vs. focus on teachers, Focus on learners through focus on teachers, etc. Thus, we proposed to emphasize the duality of the roles of learners and teachers in the educational process, and this call received many different and interesting reactions.

Our three plenary speakers are prominent figures from the three countries of North America. Luis Radford from Ontario’s Université Laurentienne will use a semiotic point of view to study the algebraic thinking. Marta Civil of the University of Arizona will tackle the issue of equity by focusing not only on learners and teachers but also on parents. Tenoch Cedillo of the Mexican Universidad Pedagógica Nacional will propose a way in which teachers can –and do– learn from students. Not less notorious are the three personalities that have been selected to react to these plenary presentations: Carolyn Kieran from the Université du Québec à Montreal, Arthur Powell from Rutgers University, and Sharon Senk from Michigan State University. (We have been fortunate enough to have Carolyn Kieran’s reaction paper in time for publication; the other two are unfortunately not included in the proceedings but will undoubtedly also cast a lucid light upon the topics that will be approached).

We will have six of the Working Groups that have been productively working for the last years, and engaging in topics from the complexity of learning to reason probabilistically to gender and mathematics, from in-service teacher education and teaching assistant preparation to the mathematics classroom discourse, and of course the classic WG on models and modeling. Two new Discussion Groups are proposed this year, which will certainly add to the interest and quality of the reunion: one on the lesson study and one on transnational issues in mathematics education.

After the plenary sessions and the WG and DG, which comprise the first volume of the proceedings, the second one displays the 240 Research Reports, Short Oral Reports and Posters of the traditional fifteen topics (this year the topics of Rational Numbers and Whole Numbers have been put together in one). It may be pointed out that this year we received more than 350 proposals, which unfortunately contrasted with the very limited amount of rooms available in the Conference’s venue; in order to give as many people as possible the space and time for their presentations we decided on the following distribution: 28% Research Reports, 34% Short Oral Reports, and 38% Posters. As a consequence of this, we are sure that all the sessions will excel; for instance, our two sessions of posters are very promising.

This is the general overview of the papers included in these proceedings. Their richness, however, will begin to be appreciated during the Conference, in the presentations and in the following discussions. And, of course, the quality of the presented papers, the fruitfulness of the discussions and the interaction with international researchers will without doubt benefit the Mexican Mathematics Education community.

I would like to thank all the authors of proposals for contributing with such samples of good work, and also the reviewers for taking time to carefully read the proposals and give their professional opinion on them. I also wish to thank the Steering Committee for all their support, good advise, and thoughtful work throughout this year. The Local Committee has certainly been fundamental in taking this car to a good end; my gratitude to all of them. Last, but not least, the Universidad Pegagógica Nacional, host of the Conference, has given all sorts of backing to make this event come true. I wish to thank very specially the Head of the University, Marcela Santillán Nieto, for her full support.

Silvia Alatorre
Program Chair