This study assessed the impact of inquiry-demonstration method on remediating Newman errors in quadratic equations and enhancing performance in algebra among senior secondary students in Kaduna state. The research design was survey and quasi-experimental in nature. Diagnostic test for Newman errors identification was surveyed while; the remediating part was in form of quasi-experimental in nature. Pre-test posttest experimental and control group design was adopted. Two Co-educational schools were selected out of twenty senior secondary schools in the zone. 186 students made up of 113 males and 73 females out of 3,606 senior secondary school students were randomly selected as sample size and used for the study. Four research questions and four hypotheses were formulated and assessed using descriptive statistics of frequency and percentage to answer research questions 1, 2 and 3. Mean and standard deviation was used to answer research question four. Chi-square statistics was used to test null hypotheses 1, 2 and 3 and t-test statistics was used to test null hypothesis 4, ANOVA was used to test the significant difference among schools and Schaffer's was used to test those schools that were not significant as sample schools, at P ≤0.05 level of Significance. Three instruments were used, Quadratic Equation Error Diagnostic Test (QEDT), Quadratic Equation Performance Test, and Modified Newman Interactive Schedule (MNIS) to measure the Newman errors, Performance as well as conducting an interactive schedule. Test retest reliability was observed. Pearson Product-Moment Correlation Coefficient (PPMCC) Statistics of the instruments was used to estimate the reliability coefficients and calculated to be 0.88 and 0.75 respectively. The difficulty and discriminating indices were found to be 0.80, and 0.71. The findings showed that there was significant difference in the frequencies of Neman errors of experimental and control groups, the inquiry-demonstration method of teaching was not gender friendly on Newman errors and performance. It is recommended that provision of in-service training on the effective use of inquiry-demonstration method in the teaching and learning processes of quadratic equation in algebra be granted to teachers, to minimize the Newman errors and improve students' performance in mathematics, the concepts of quadratic equations in algebra should be taught effectively in order to reduce the frequencies of Newman errors and improve students' performance. Professional bodies such as MAN, STAN, Mathematics educators, Text books publishers should organize training programs for teachers teaching mathematics in form of seminars, workshops and conferences focusing on the effective use of inquiry-demonstration method as an instructional strategy in the teaching and learning of the concepts of algebra in mathematics