The purpose of this study was to examine the relationship between parental involvement and students' academic achievement in Model Primary and Secondary School of Haramaya University, Oromia Regional State, Ethiopia. Correlational research design was employed to carry out the current study. Questionnaire interview and document analysis were employed to was employed to collect the data from selected respondents. The sample consists of 52 parents and 60 students purposively selected. The students were selected by their academic rank which means 50% were high achievers whereas below50% were lower achievers from the 8th, 10th and 12th grades. Parents of 30 top scoring and 30 low scoring students were selected purposively. Parental involvement was measured by using self-developed questionnaire with 10 items and eight interview guide questions were used, and students' academic achievement was measured by their recorded scores by their respective grades in the past three years four interview guide questions were employed. The first finding was that there was statistically significant positive relationship between parental involvement and students' academic achievement, (r=0.64, p<0.01). The second finding was that the portrayed students who ranked from 1st to 10th from grades 8, 10 and 12 were highly involved, supported and followed by their parents on their education. The third finding was that students who were scored below 50% and ranked last 10's from perspective grades were children whose families were less encouraged and involved. In general, parents' involvement in supporting their students to boost their academic achievement is moderate. It is recommended that more detailed studies can be conducted in the future in different areas as well as country wide.