Background: One of the objectives of the new Spanish Education Act is for students to develop a series of social skills, largely derived from the ability variables of assertiveness and empathy. Sport Education is an instructional model that is deemed useful in the development of personal and social responsibility and social values. It requires interaction among students during group activities as there are many roles and responsibilities involved. Previous research on Sport Education reveals links between certain results and empathy and assertiveness, although no specific studies have been conducted. Purpose: The aim of this research study is to analyse the effect of a Sport Education season on student empathy and assertiveness. Participants and setting: Sport Education was implemented in seven intact groups at five different schools in central Spain. 154 subjects (76 boys and 78 girls) participated in this study, 34 of whom were in primary education year 5 (11 years), 98 in primary education year 6 (12 years) and 22 in secondary education year 2 (14 years). Research design: A single treatment pre-post-test design was applied, in which the tests for measuring the dependent variables (empathy and assertiveness) influenced by the independent variable (the Sport Education season) were applied before, during and at the end of the programme. Data collection: The Empathy Questionnaire and the Children's Assertiveness Behaviour Scale were used to measure dependent variables. Data analysis: For group/team data, analysis of variance was conducted to determine the influence of Sport Education on empathy and assertiveness. For individual students, repeated measures analysis of variance were utilised to measure the influence of factors, such as gender and role at the various points at which the programme was applied (pre-test and post-test). Findings: Positive results were obtained in assertiveness, where differences were significant between pre-test and post-test, although the effect size differed from case to case. Group and team were key aspects when differences were significant. Conclusions and implications: Sport Education was shown to be a useful instructional model for improving a variable (assertiveness) directly related to personal and social responsibility. Nevertheless, in order to achieve these results, teachers need to design and apply pedagogical strategies routinely, and pay very close attention to the dynamics created in the classroom. Further research involving more specific testing of classroom situations in general and Physical Education situations in particular is also required.