The purpose of this study is to investigate the effect of using web-based curricula on seventh grade students' achievement in mathematics in King Abdullah School in Irbid, Jordan. The researcher followed the equivalent pre/post T-test two group designs. To achieve the aim of the study, a pre/post-test was constructed to measure students' achievement in mathematics. The test consisted of twenty five questions on statistics and probability. The sample of the study comprised of (148) seventh grade students, they were 37 male students for the experimental group and 33 male students for the control group, while the female students for the experimental and control group were 38 and 40 respectively from King Abdullah School in Irbid during the first semester of the scholastic year 2009/2010. Descriptive statistical analyses were used (means and standard deviation) for the pre and post- tests of students' mathematical test to experimental and control groups. Comparison statistical methods were used (Two Way ANOVA) analysis of variance to make a comparison between the control and the experimental groups, gender variable (male and female), and interaction between them. The findings of the study indicated that there were statistically significant differences in the post-test between the control and the experimental groups in favor of the experimental group, and there was no statistically significant difference in the students' achievement due to gender. There was no statistically significant difference due to the interaction between gender and group. The researcher proposed some recommendations to enhance the effect of using performance-based assessment on students' language accuracy such as conducting further studies on other populations and for a longer time. (Contains 4 tables.)