The purpose of the study was to identify, analyze and compare the concord use errors in the written and structural tests of Diploma 1 students of J.S.C.O.E, Gumel and Jigawa State Polytechnic, Dutse. It examined the error types, frequency of occurrence and provided strategies and recommendations to minimize their re-occurrence. One essay test and one structural test were administered and the identified errors analyzed and compared. The concord use errors by the sampled students were obtained. For data analysis, percentage, means and standard deviations were used to answer the research questions. Independent samples T-test analysis was used to test hypotheses used in the study respectively. Descriptive research design was also used. The study area has a population of 265 for 2015/2016. A sample size of 155(Diploma 1 students) were used according to sample size published by Krejcie and Morgan (1980). Eighty (80) students from J.S.C.O.E, Gumel and seventy five (75) from J.S.P, Dutse were sampled through random sampling technique. Two researcher-designed instruments were modified and used from J.S. Digga (1990); Concord Use Structural Test (CUST) and Concord Use Written Test (CUWT). The data were presented in tables and simple percentages accompanied by explanatory and descriptive analyses on the basis of which conclusions were drawn. For the concord use written test, the mean difference was 2.427. The statistical tool used for data interpretation was the independent t-test, tested at 0.05% level. The findings indicated that, a significant difference in the mean concord use errors of Diploma 1 students was found in their written essays. However, there was no significant difference in the subject-verb concord use errors among Diploma 1 students of C.O.E and Poly respectively. Furthermore, the findings revealed no significant difference in the mean pronoun-antecedent concord use errors among the students. There was significant difference in the mean tense concord use errors by the students. The findings also showed that out of the three major categories of concord use errors, tense errors ranked highest. This was followed by subject-verb concord use errors and then pronoun-antecedent concord use errors. Students tended to avoid the use of passive voice and phrasal verbs. The frequencies of errors committed have a direct negative effect on the academic achievements of students. The study concludes that the remedial measures and strategies could be used to improve the situation were recommended.