Traditional teaching strategies dominate science classrooms in Lesotho, resulting in poor academic performance at each level. Information and Communication Technology tools such as simulations offer potential benefits for improving science teaching. The purpose of this quasi-experimental study was to evaluate the effect of simulations on learners' performance and retention of stoichiometry concepts using Solomon's four-group design. Purposive sampling of two existing Form E (Grade 12) classes, with 81 learners, led to the creation of four groups. The study responds to the research question: How does using simulations as part of an intervention affect learners' academic performance in stoichiometry? Data were collected as learners' scores for pre-tests and post-tests, designed to assess their understanding of stoichiometry, and analysed through ANOVA and t-tests. After the intervention, the experimental group's mean score (M = 44.2, a = 18) was higher than that of control group (M = 32.6, a = 15.8), and the difference between the two mean scores was statistically significant, namely t(81) = 3.14, p = 0.002. The experimental group had a higher mean score for retention in post-test (M = 47.4, a =16.1) than the control group (M = 37.2, a = 13.7) which was statistically significant, namely t(81) = 3.10, p = 0.003. Therefore, it was concluded that simulations enhanced learners' performance and could improve the retention of stoichiometry concepts. This study recommends that simulations be used to supplement the teaching and learning of science, in particular chemistry. Keywords: cognitive theory of multimedia learning, high school learners' performance, interactive-simulations, stoichiometry

The unique nature of online teaching and learning has its own affordances and challenges. The purpose of this study was to assess science pre-service teachers’ perceptions about efficiency of online teaching and learning in science after experiencing it first-hand during the hard lockdowns due to Covid-19 pandemic. Mixed methods approach, with closed and open-ended questionnaires, was adopted to establish: What perceptions the pre-service teachers have about online teaching and learning in respect of effective teaching and effective assessment? What correlations can be drawn from pre-service science teachers experience of online teaching and learning with their perceptions? And to what extent this mode of teaching prepared these pre-service teachers to use it in their teaching practice? Descriptive statistics and content analysis of data revealed that participants rated online teaching and learning low and had a challenging experience in terms of collaboration, access to material and making meanings out of some science concepts. Participants reported low confidence relating to perceived ease of use and perceived usefulness of online teaching and learning. The study concludes that the harsh experiences were the main contributing factors to the observed perceptions of participants as neither the lecturers nor these student-teachers were prepared for this mode of teaching and learning. Therefore, this study recommends that support mechanisms for students should be made available for online teaching and learning even under emergency situations. Pre-service teachers should also be given a chance to experience online teaching and learning under normal circumstances if they are to incorporate it in their teaching.