Having observed the reckless abandonment of professional codes and ethics of teaching soon after certification, and specifically the subterfuge of the use of instructional materials in lesson delivery, the researchers set out to investigate the state-of-the-art in terms of availability and use of mathematical instructional materials, and the influence of these on students’ achievement in the subject. Three instruments, a 20-item Mathematics Teacher Instructional Materials Availability Questionnaire (TIMAQ), a 20-item Mathematics Teacher Instructional Material Use Questionnaire (TIMUQ) and a 30-item Multiple Choice Achievement Test (MCAT) were developed, validated (test-retest reliability coefficients of 0.87 and 0.97 respectively for TIMAQ and TIMUQ, and KR-20 coefficient of 0.89 with mean 40.8, S.D. 11.33) for MCAT. Two hundred (200) students (20 per school comprising 100 male and 100 female) were selected from the ten public secondary schools in Akamkpa Local Government Area by stratified random technique, and two (2) Mathematics teachers per school for the study. Results of the simple percentage and independent t-test analyses revealed the non-availability and non use of instructional materials in Mathematics instruction, as well as significant achievement differences between materials-available and non-available schools on one hand and achievement of students from material-used and non–used schools on the other. Useful recommendations were therefore made based on these findings.Keywords: mathematics instructional materials, students’ achievement, availability of instructional materials, use of instructional materials