This study investigated the effectiveness of prior knowledge of instructional objectives on the academic achievement of Electrical Installation and Maintenance Works students. Two research questions and two hypotheses guided the study. The design of the study was pre-test, post-test, non-equivalent control group quasi experimental study. The study was carried out in Enugu State in the present South East Zone of Nigeria. The population for the study was 1,115 year two Electrical Installation and Maintenance works students in the 19 technical colleges in the State. One technical college which offers Electrical Installation and Maintenance works was randomly chosen from the six educational zones in the State for the study. The total number of students in their intact classes who offered Electrical Installation and Maintenance works in these colleges was 326. This formed the sample for the study. 249 (79.4%) of the students were male and 77 (23.6%) were females. The instrument used for data collection was the Electrical Installation and Maintenance Achievement Test (EIMWAT). This had two versions Pre-test and Post-test which were the same except for the swapping of all the options for each answer for the 30 questions used for the study. The instrument was subjected to both face and content validation and item analysis. The reliability of the instrument was established Using Kuder Richardson (K-K) 20, the internal consistency was found to be 0.78 using Pearson r, the test retest stability measure was found to be 0.96. Pre-EIMWAT was administered by the beginning of the five weeks treatment period. Post EIMWAT was administered at the end of the five weeks treatment period. Scores from Pre-EIMWAT, Post-EIMWAT tests were analyzed using means, standard deviation and Analysis of Covariance (ANCOVA). The major finding from the analysis was that prior knowledge of instructional objectives before instruction was more effective in student’s academic achievement than the conventional method of teaching. The study recommended that (i) teachers should not only state instructional objectives but expose them to students before instruction and refer same to them at intervals during their teachings; (ii) the use of prior knowledge of instructional objectives for instruction should be given greater emphasis by teachers because of its general effectiveness on retention.