Among all approaches aimed at reducing poor mathematics achievement among the students, adoption of appropriate methods of teaching appears to be more rewarding. In this study, improvised instructional materials were used to ascertain students' geometry achievement at the upper basic education one. Two research questions were asked with associated two hypotheses tested at 0.05 level of significance. It adopted a quasi-experimental design of non-randomised pre-test post-test control group type. The research was carried out at Makurdi metropolis with a population of 1680 Universal Basic Education (UBE) students. From this, 139 students were sampled from four schools out of the 22 UBE schools. Instrument of the study was Geometry Achievement Test (GAT). Research questions asked were answered using descriptive statistic of mean and standard deviation while the hypotheses formulated were tested at 0.05 level of significance using Analysis of covariance. The study found that student's were taught with improvised instructional materials. Also that both male and female in the experimental group equally improved upon their geometry achievement over those of the control group. Recommendations such as encouraging mathematics teachers to use improvised instructional materials in their mathematics classroom were made among others. Relevant and adequate conclusions were also made.