Background: To develop pupils' team invasion games (TIG) performance within physical education (PE), practitioners have traditionally adopted teacher-centred, skill-focused approaches. Teaching Games for Understanding and the Tactical approach are alternative approaches to TIG teaching that aim to develop overall game performance, including decision-making performance. Purpose: The main purpose of this study was to conduct an ecologically valid investigation into the effects a tactical teaching approach had on game knowledge, game playing performance and pupil perception of decision-making ability compared to authentic teaching in a Scottish secondary school. Participants and setting: Fifty-two pupils (24 female; 28 male; age = 12.5 plus or minus 0.3 years) participated in this study. The pupils were made up of two secondary 1 (S1) classes from a Scottish urban state secondary school. Both classes were heterogeneous in terms of gender and ability and the pupils from each class had similar pre-secondary school PE experiences. Two teachers, Lisa and Anthony, took part in this study. Both Lisa (age = 23 years) and Anthony (age = 27 years) had taught in the school for one year. Intervention: The overall aim for both teachers was to develop the pupils' performance in a game of 4v4 basketball over a five-week block. The teaching strategies Lisa used to reach this aim were based on the Tactical approach to teaching games. Using pupil-centred teaching strategies such as problem-solving, discussing and reflecting, Lisa's aims were to develop the pupils' tactical understanding and game performance in relation to creating space on and off-the-ball to keep possession and progress towards target, re-gaining possession and counter attack, and denying space in the key area. Anthony followed the PE department's guidelines for teaching basketball to improve the pupils' performance in 4v4 basketball. This involved the application of direct teaching strategies to teach the chest pass, the bounce pas, dribbling, the set shot, the jump shot and the lay-up. Data collection: Data from focus group interviews was gathered in order to elicit pupils' knowledge and experiences of learning to play TIG. The pupils were recorded on video before and after the intervention to determine any differences in game playing performance between groups. Finally, a questionnaire was administered in order to establish the pupils' perception of their own decision-making abilities both on and off-the-ball. Data analysis: The focus group interview data were analysed by two experienced researchers who identified key experiences (or bodies of knowledge) about basketball that the pupils in each group discussed. In order to analyse the participants' game performance in offence both on and off-the-ball, their tactical decisions were coded as "good" or "poor", and their on-the-ball skill execution was coded as either "successful" or "unsuccessful". The questionnaire data were analysed using a mixed design two-way repeated measures ANOVA to test for differences between the two groups in their perception of decision-making ability. Findings: During the focus group interviews, the group that took part in the traditional, more skill-focused, lessons discussed the technical components of basketball skills, and the pupils from the game-based lessons discussed the different principles of play that they applied during practices and games. The 4v4 game performance data demonstrated that the game-based group made significantly more good decisions on and off-the-ball compared to the skill-focused group. There were no significant differences between groups post intervention in terms of on-the-ball skill execution. The pupils in the game-based group believed that their decision-making abilities, both on and off the ball, had improved. In contrast, the class that took part in the skill-focused lessons believed that their decision-making abilities had deteriorated over the five-week period. Conclusion: The findings from this research provide valuable information in relation to the learning outcomes produced by different teaching approaches during an investigation high in ecological validity. In order to further our understanding teaching TIG, future research should examine the teaching and learning processes involved when adopting such approaches. (Contains 1 figure and 6 tables.)