The world we live in is increasingly multimodal, necessitating multiliteracy for learners to engage meaningfully with knowledge and skills. While verbal language is the primary medium for constructing, communicating and learning scientific knowledge and concepts, visuals can help learners to gain knowledge that they may not develop from verbal explanations alone. Verbal and visual semiotic modes have the potential to function in a complementary way, working together to strengthen meaning. This paper explores the dynamics of verbal–visual intersemiotic complementarity in the classroom practice of three junior secondary physical science teachers in the Oshana region of Namibia. It reports on a qualitative case study employing Systemic Functional Linguistics in the analysis of multimodal discourse. The results revealed how the content selections in the verbal and visual modes of the science teachers’ practice are related in terms of the meanings and their relationships through all five intersemiotic sense relations. The results also showed that some teachers consistently employed fewer visuals. The results further highlighted low frequency of the use of intersemiotic antonymy (opposites) and hyponymy (hierarchy) by each teacher compared with intersemiotic repetition, synonymy (synonyms) and meronymy (whole–part relationships). It is recommended that Namibian science teacher training programmes incorporate intersemiotic complementarity in order to help teachers harness the full potential of this approach.

我们生活的世界越来越多峰，需要多种语言才能使学习者有意义地参与知识和技能的学习。言语是构建，交流和学习科学知识和概念的主要媒介，而视觉可以帮助学习者获得知识，而这些知识可能不会仅凭言语解释而发展。言语和视觉符号模式有可能以互补的方式发挥作用，共同增强含义。本文探讨了纳米比亚奥沙那地区三名初中物理科学教师在课堂实践中言语-视觉符号间互补性的动态。它报告了使用系统功能语言学分析多模态话语的定性案例研究。结果表明，通过所有五个符号间意义的关系，理科教师的言语和视觉方式中的内容选择在意义及其关系方面是如何关联的。结果还表明，一些教师始终采用较少的视觉效果。结果进一步表明，与符号间重复，同义词（同义词）和代名词（全部分关系）相比，每位教师使用符号间反义词（对立）和下位格（层次结构）的频率较低。建议纳米比亚科学教师培训计划纳入符号间的互补性，以帮助教师充分利用这种方法的潜力。