This study aims to determine the effect of science teaching according to the guided inquiry-based learning approach on the academic achievement and conceptual understanding of middle school grade 8 students. The study sample consists of a total of 48 students, including 22 in the experimental group and 26 in the control group, studying at Mezre middle school in the city center of Elazıg in the 2020-2021 academic year. In the study, the Electrical Energy Unit Achievement Test and the Electrical Energy Unit Conceptual Understanding Test were used as data collection tools. A quasi-experimental design with a pre-test and post-test control group was used in the study. The analysis of the data in the study was made with the SPSS 21.0 statistical program. Data normality distributions were checked by looking at the skewness and kurtosis values. Since the data did not show a normal distribution, the data obtained in the study were analyzed using the Wilcoxon Signed Ranks Test and the Mann-Whitney U-test. When the analysis findings were examined, it was seen that there was a statistically significant difference in favor of the experimental group between the post-test scores of the achievement test and the conceptual understanding test regarding the electrical energy unit of the middle school grade 8 students in the experimental and control groups. This finding shows that teaching the electric energy unit according to the guided inquiry-based learning approach positively increases the academic achievement and conceptual understanding levels of the grade 8 students in the experimental group, and it is an effective approach.