Purpose: Recent trends have encouraged the use of alternative assessment tools in class in line with the recommendations made by the updated curricula. It is of great importance to understand how alternative assessment affects students' academic outcomes and which techniques are most effective in which contexts. This study aims to examine the impact of alternative assessment techniques on achievement. Research Methods: In the study, a meta-analysis was conducted to combine the effect sizes of the primary studies during data collection and data analysis. Findings: Data analysis indicated that alternative assessment techniques have a significant and positive effect (d = 0.84) on students' academic achievement. Such techniques have been found to be more effective in Mathematics courses (d = 0.84), and the effect of using portfolios in class (d = 1.01) is worthy of note. In accordance with the moderator analysis, whereas the effect sizes do not significantly vary in terms of subject matter and type of alternative assessment technique, there is a significant difference in the effect sizes in terms of school levels of students. Implications for Research and Practice: The results highlighted portfolios as a highly effective assessment technique for students' academic achievements, and it revealed the impact of alternative assessment techniques on enhancing academic outcome. However, the low effectiveness of authentic assessment at the primary level may be associated with the development of creativity and critical thinking skills over time.