The purpose of this study was to investigate the effect of fixed vs floating facilitator approaches of Problem-Based Learning (PBL) on students' achievement and interest in Elementary Structural Design (ESD). The design was quasi-experimental with a pretest-posttest nonequivalent 2 × 2 factorial design. The participants (78) were randomized to treatment conditions. The researchers conducted a repeated-measures analysis of variance and univariate analysis of variance to compare changes across the treatment groups. Results show that using the fixed facilitator model of PBL approaches is more effective in improving students' achievement, while both models increase students' interest in elementary structural design (ESD). Also, the study revealed that there was no influence attributable to gender on students' achievement and interest in ESD. Hence, the fixed facilitator instructional model was advocated for technical teachers to foster students' achievement and interest in ESD in Nigeria.