The study determined the effects of teacher constructivist model and interest on students academic achievement in fabrication and welding in technical colleges in Lagos state. The study is a pre-test, post-test involving students in two groups:namely Experimental and control groups. Two research questions and two hypotheses guided the study and tested at 0.05 level of significance. The population and sample of the study consists of all the 80 National Technical Certificate (NTC) 11 students offering fabrication and welding in the four technical colleges selected. The instruments used for data collection were the Fabrication and Welding Achievement Test (FWAT) and Fabrication and Welding Interest Inventory (FWII). The reliability co-efficient using Cronbach alpha for interest and Kuder-Richardson for achievement yields 0.76 and 0.74 respectively. Mean and Standard deviation were used to answer the research questions, while Z-score was used to test the hypotheses. Based on the findings, students thought with teacher constructivist model performed better than those taught with conventional teaching method, and also have higher interest in fabrication and welding. Recommendation were made pertaining to the findings of the study.