This study investigated the perceived impacts of formal and informal mentoring practices among teachers of English language in secondary schools in North West, Nigeria. The study used descriptive survey research design. The population of the study was 891 teachers of English language. A sample size of 269 was estimated by the Research Advisor’s 2006 table for determining sample size. This sample was achieved through a multistage sampling technique. A Perceived Impact of Mentoring Practices Questionnaire (PIMPQ), a Structured Interview, and a Non-Participant Observation Checklist were the instruments used in the study. The instruments were validated by a senior lecturer of Language Education, Department of Curriculum Studies and Educational Technology, a senior lecturer of measurement and evaluation from the Department of Science and Vocational Education, Usmanu Danfodiyo University, Sokoto and a seasoned English language teacher from Nagarta College, Sokoto. The instruments were pilot-tested at Nagarta College, Sokoto. In to assessing the internal consistency of the instruments, Cronbach’s alpha reliability coefficient was calculated at r = 0.87. Data collected was analysed through descriptive statistics of means and standard deviation on Statistical Package for Social Science (SPSS) version 25 to answer research questions and inferential statistics of Wilcoxon Signed Ranks were used to test all the null hypotheses at a 0.05 level of significance. The results showed that formal mentoring was perceived to be more beneficial in improving English language teaching by providing structured learning opportunities and direct support to teachers over informal mentoring and there was a statistically significant difference between teachers’ perception of the impacts of formal mentoring over informal mentoring, with formal mentoring having a higher impact. It therefore recommended that formal mentoring should be encouraged among teachers of the English language in North West, Nigeria.