The purpose of the study was to develop and validate math readiness test for measuring readiness level of senior secondary school one (SSI) entrants. The population of the study was 5403. 300 beginning SSI students were randomly sampled from the population. The instrument developed and used for the study was math readiness test (MATHRET). 6 research questions and 3 hypotheses guided the study (P.05). Reliability coefficient of 0.91 was obtained using Kuder Richardson (KR-20). Mean and percentage were used in answering the research questions and t-test in testing the hypotheses. Findings: 0.91 reliability coefficient was obtained for the MATHRET, 12.67% and 15.67% were ready and fairly ready respectively while 71.66% were found not ready for the senior secondary school math work. Males were more ready than females with mean error difference of 6.53. Urban students were more ready than rural students. Students in public schools committed more errors than students in private schools with mean error difference of 3.13. It was recommended that MATHRET need to be adopted and adapted for use in junior secondary school math instruction and evaluation, among others.