The present study investigates the effect of the separator lines on the learning of 8th grade students in simplifying algebraic expressions with parenthesis. An experimental study was designed to achieve this goal involving 60 girl students in 8th Grade (13 and 14 years old) randomly selected and assigned to two experimental and control groups. After taking the pre-test, both groups were taught by one teacher. The control group was led as usual and the experimental group was taught by using the separator lines. As a result of the covid-19 disease, students were taught online using WhatsApp. In the end, a post-test was carried out for both groups. Data was also collected using WhatsApp. For the analysis of the data, a Covariance test was conducted. The results showed positive effects of separator lines on the student's performance, as well as reducing their mistakes when working with parenthesis.