This document contains the fifth volume of the proceedings of the 30th Conference of the International Group for the Psychology of Mathematics Education. Conference presentations are centered around the theme "Mathematics at the Centre." This volume features 59 research reports by presenters with last names beginning between Sac and Zaz: (1) Bryan's Story: Classroom Miscommunication about General Symbolic Notation and the Emergence of a Conjecture during a CAS-Based Algebra Activity (Ana Isabel Sacristan and Carolyn Kieran); (2) A Teacher's Method to Introduce Story-Problems: Student-Generated Problems (Adalira Saenz-Ludlow); (3) "There's More than Meets the Eye": Analysing Verbal Protocols, Gazes and Sketches on External Mathematical Representations (Jonathan P. San Diego, James Aczel, Barbara Hodgson, and Eileen Scanlon); (4) Notions of Variability in Chance Settings (Ernesto Sanchez and Miguel Mercado Martinez); (5) Elementary Preservice Teacher Learning Levels (Victoria Sanchez and Miguel Mercado Martinez); (6) Mathematics Achievement: Sex Differences vs. Gender Differences (Dora Santos, Sonia Ursini, Martha Patricia Ramirez, and Gabriel Sanchez); (7) Self Assessment and Appropriation of Assessment Criteria (Leonor Santos and Anabela Gomes); (8) Drawing as Problem-Solving: Young Children's Mathematical Reasoning through Pictures (Carole Saundry and Cynthia Nicol); (9) The Role of the Teacher in Turning Claims to Arguments (Baruch Schwarz, Rina Hershkowitz, and Shirly Azmon); (10) Learning Mathematics for Teaching (Nanette Seago and Lynn Goldsmith); (11) Coherence of Mathematics Lessons in Japanese Eighth-Grade Classrooms (Yasuhiro Sekiguchi); (12) Triangle Property Relationships: Making the Connections (Penelope Serow); (13) Access to Mathematics versus Access to the Language of Power (Mamokgethi Setati); (14) Compartmentalization of Representation in Tasks Related to Addition and Subtraction Using the Number Line (Myria Shiakalli and Athanasios Gagatsis); (15)The Derivation of a Learning Assessment Framework for Multiplicative Thinking (Dianne Siemon, John Izard, Margarita Breed, and Jo Virgona); (16) Sources of Students' Frustration in Bridging Mathematics Courses (Anna Sierpinska); (17) What Makes a Good Problem? An Aesthetic Lens (Nathalie Sinclair and Sandra Crespo); (18) Discovering a Rule and Its Mathematical Justification in Modeling Activities Using Spreadsheet (Hong-chan Son and Hee-chan Lew); (19) Investigating Preservice Teachers' Understanding and Strategies on a Student's Errors of Reflective Symmetry (Ji-Won Son); (20) Exploring the Role Played by the Remainder in the Solution of Division Problems (Alina Galvao Spinillo and Sintria Labres Lautert); (21) Incomplete or Incorrect Understanding of Decimals: An Important Deficit for Student Nurses (Vicki Steinle and Robyn Pierce); (22) Proportional Reasoning: Variable Influencing the Problems Difficulty Level and One's Use of Problem Solving Strategies (Olof Bjorg Steinthorsdottir); (23) The Impact of the Intuitive Rule "If A Then B, If Not A Then Not B" in Perimeter and Area Tasks (Lambros Stephanou and Demetra Pitta-Pantazi); (24) Process-Object Difficulties in Linear Algebra: Eigenvalues and Eigenvectors (Sepideh Stewart and Michael O. J. Thomas); (25) Conceptual Changes as Dialectical Transformation (Nadia Stoyanova Kennedy); (26) Content Knowledge for Mathematics Teaching: The Case of Reasoning and Proving (Andreas J. Stylianides and Gabriel J. Stylianides); (27) "Making Proof Central to Pre-High School Mathematics Is an Appropriate Instructional Goal": Provable, Refutable, or Undecidable Proposition? (Gabriel J. Stylianides and Andreas J. Stylianides); (28) Power and Poverty--Whose, Where, and Why?: School Mathematics, Context and the Social Construction of "Disadvantage" (Dalene M. Swanson); (29) Documenting Learning in School-Based Mathematics Communities of Teachers (Paola Sztajn); (30) Research and Teaching--Can One Person Do Both? A Case Study (MichalTabach); (31) Computer "Knowledge" and Student's Images of Figures: The Case of Dragging (Varda Talmon and Michal Yerushalmy); (32) Graphics Calculators for Mathematics Learning in Singapore and Victoria (Australia): Teachers' Views (Hazel Tan and Helen J. Forgasz); (33) Vague Language in Greek and English Mathematical Talk: A Variation Study in Face-Work (Konstantinos Tatsis and Tim Rowland); (34) Teachers Using Computers in Mathematics: A Longitudinal Study (Michael O. J. Thomas); (35) Analysing Classroom Interactions Using Critical Discourse Analysis (Steve Thornton and Noemi Reynolds); (36) Pre-Service and In-Service Mathematics Teachers' Concept Images of Radian (Tahsin Topcu, Mahmut Kertil, Hatice Akkoc, Kamil Yilmaz, and Osman Onder); (37) Adaptive Expertise in the Number Domain 20-100 (Joke Torbeyns, Lien Vanderveken, Lieven Verschaffel, and Pol Ghesquiere); (38) Mathematical Activity in a Technological Workplace: Results from an Ethnographic Study (Chrissavgi Triantafillou and Despina Potari); (39) Pupils' Over-Use of Proportionality on Missing-Value Problems: How Numbers May Change Solutions (Wim Van Dooren, Dirk De Bock, Marleen Evers, and Lieven Verschaffel); (40) Arithmetical Procedures in the Solution of a Problem Involving Velocity (Veronica Vargas and Jose Guzman); (41) Introducing Algebraic Thinking to 13 Year-Old Students: The Case of the Inequality (Petros Verikios and Vassiliki Farmaki); (42) Why Is a Discontinuous Function Differentiable? (Antti Viholainen); (43) Overgeneralization of Linear Models: Presence and Characteristics among University Students (Monica Villareal, Cristina Esteley, and Humberto Alagia); (44) Educational Design Research in Mozambique: Starting Mathematics from Authentic Resources (Pauline Vos, Tiago G. Devesse, and Assane Rassul); (45) "The Big Test": A School Community Experiences Standardized Mathematics Assessment (Fiona Walls); (46) Numeracy Reform in New Zealand: Factors that Influence Classroom Enactment (Margaret Walshaw and Glenda Anthony); (47) An Investigation of Factors Influencing Teachers' Scoring Student Responses to Mathematics Constructed-Response Assessment Tasks (Ning Wang and Jinfa Cai); (48) Teacher Actions that Assist Young Students to Write Generalizations in Words and in Symbols (Elizabeth Warren); (49) Promoting Pre-Service Teachers' Understanding of Decimal Notation and Its Teaching (Wanty Widjaja and Kaye Stacey); (50) Impetus to Explore: Approaching Operational Deficiency Optimistically (Gaye Williams); (51) Generating and Evaluating Geometry Conjectures with Self-Directed Experiments (Chao-Jung Wu, Wing-Kwong Wong, Ying-Hao Cheng, and Yunn-Wen Lien); (52) The Distributions of van Hiele Levels of Geometric Thinking among 1st and 6th Graders (Der-bang Wu and Hsiu-Ian Ma); (53) Elementary Teacher Education and Teacher Efficacy toward Mathematics and Science (Su-Chiao Wu and Yu Liang Chang); (54) Spatial Rotation and Perspective Taking Abilities in Relation to Performance in Reflective Symmetry Tasks (Xenia Xistouri and Demetra Pitta-Pantazi); (55) Elementary Teachers' Mathematics Beliefs and Teaching Practices after a Curriculum Reform (Shirley M. Yates); (56) Inquiry Activities in a Classroom: Extra-Logical Processes of Illumination vs. Logical Process of Deductive and Inductive Reasoning. A Case Study (Oleksiy Yevdokimov); (57) Developments of a Child's Fraction Concepts with the Help of Psychological Tools: A Vygotsky's Cultural-Historical Perspective (Kaori Yoshida); (58) A Teacher's Treatment of Examples as Reflection of Her Knowledge-Base (Orit Zaslavsky, Guershon Harel, and Alfred Manaster); and (59) Cognitive Conflict and its Resolution via Pivotal/Bridging Example (Rina Zazkis and Egan Chernoff). (Individual papers contain references.).