Background: Homework is a common educational task given to students around the world. It demands mental exertion, but staying focused can be challenging, especially for K-12 students. Too much homework can increase their cognitive load and mental fatigue, leading to decreased motivation and performance. This can cause boredom with homework and learning. To lessen their load and make homework more effective, it is important to establish the connection between homework duration and academic achievement. Objectives: To evaluate the relationship between homework time and academic performance among K-12 students. Search Methods: On November 5, 2021, we retrieved articles from a variety sources. Firstly, we searched 10 electronic databases for related publications, including Academic Search Premier, APA PsycArticles, APA PsycInfo, Business Source Premier, Education Resources Information Center (ERIC), Journal Storage (JSTOR), Learning and Technology Library (LearnTechLib), OCLC FirstSearch, Social Sciences Citation Index (Web of Science), and Teacher Reference Center. We also searched two publisher platforms: ScienceDirect and Taylor & Francis Online Database. Secondly, we consulted five educational organization website such as, American Educational Research Association, Best Evidence Encyclopedia, Education Endowment Foundation, European Educational Research Association, What Works Clearinghouse, and the Open Grey database for unpublished studies. We then searched Open Dissertations and ProQuest Dissertations & Theses Global databases to locate the relevant dissertations and theses. Additionally, we hand-searched seven educational journals to identify unpublished documents, reports, and potential studies not indexed in the databases. Lastly, we searched Campbell Library to identify relevant reviews and primary (and nearly eligible studies) in these reviews. We also searched Google Scholar for related studies and checked the citations of eligible studies as well as their bibliographies. Selection Criteria: Studies with the following criteria were included: - Population: K-12 school students with no disabilities or not attending special education schools; - Intervention: Homework assigned regularly by schoolteachers to students to complete during non-school hours; - Comparison: Different time spent on the homework; - Outcomes: Academic performance was the primary outcome. The secondary outcomes were academic motivation and the quality of homework; - Study design: Treatment-control group design or comparison group design studies. Data Collection and Analysis: We reviewed the titles, abstracts, and full texts of the retrieved records. Our team extracted and coded all relevant information from the studies that met our inclusion criteria. To evaluate the risk of bias, we used the Cochrane Risk of Bias tool for randomized controlled trials and ROBINS-I for non- randomized controlled trials. A random-effect meta-analysis was conducted to determine the effect of homework on academic achievement as compared to no homework. A funnel plot, trim-and-fill method and Egger's test were used to test for any publication bias. Due to the insufficient data on homework duration and academic achievement, we analyzed these data using qualitative synthesis. Main Results: Eleven publications were identified that examined the relationship between homework duration and academic outcomes using an experimental design. Based on their focus, we categorized them into two groups: comparisons of homework with no homework and comparison of homework with less homework. There were 10 articles with 14 independent reports that compared academic performance between students who did homework and those who did not. Overall, the meta-analysis revealed that the students who did homework had better academic performance than that those who did not (n =14; g = 0.45, 95% confidence interval [CI]: 0.24-0.66; Q = 454.30, I2 2 = 71.30%, r2 2 = 0.11), especially in arithmetic computation (n = 5; g = 0.46, 95% CI: 0.17-0.75; Q =13.03, I2 2 = 69.29%, r2 2 = 0.07) and arithmetic problems solving (n = 6; g = 0.17, 95% CI: 0.02-0.33; Q = 6.87, I2 2 = 27.17%, r2 2 = 0.01), but not in arithmetic concepts (n = 3, g = -0.02, 95% CI: -0.22-0.18; Q =1.46, I2 2 = 0.00%, r2 2 = 0.00). Two experiments explored the effectiveness of homework moderated by homework time. In Koch (1965), the effects of long daily homework (20-30 min) and short daily homework (10-15 min) were compared. The authors found that achievement in arithmetic concepts was higher with long homework assignments every day. Recently, Dolean and Lervag (2021) confirmed the effect of homework on writing skills, and their findings were consistent with those of Koch (1965), who found that increasing time spent on homework was associated with greater writing achievement (average 20 min each time). Authors' Conclusions: Homework could be used as a supplement to enhance the academic performance of primary school students. However, the optimal amount of time they should dedicate each day to homework to achieve the best results remains uncertain. More high-quality experiments are needed to determine the ideal homework duration for these students. Furthermore, additional research is required to understand the impact of homework on secondary school students.
