The goal of this study was to compare the effectiveness of Web-based instruction (WBI) and traditional teaching methods on preservice elementary teachers’ fraction knowledge. Students’ knowledge of fractions was measured using a Fraction Knowledge Test. The test was administered as pre and posttests to a total of 42 preservice teachers in two classes at the same university. One of the classes was randomly assigned as the experimental group and was given WBI. The other class was assigned as a control group and was given traditional instruction. The analysis of results showed a statistically significant difference between the experimental and the control groups’ posttest mean scores in favor of the experimental group.