In educational assessment, low engagement is problematic when tests are low stakes for students but have significant consequences for teachers or schools. In the current study, we sought to establish the electroencephalographic (EEG) correlates of engagement and to distinguish engagement from mental effort. Forty university students participated in a simulated GRE General Test session while scalp EEG was recorded from 128 channels. Participants completed two verbal and two quantitative GRE test blocks for a total of 40 items each, and after each item, rated either their engagement or mental effort on a scale of 1–6. We computed power for seven frequency bands (delta, theta, alpha, beta, and low, medium, and high gamma) across six regions of interest: left hemisphere (LH) and right hemisphere (RH) frontal, temporal, and parietal. Preliminary results suggested that gamma power (30–150 hertz [Hz]) indexed differences between high- and low-engagement ratings. This pattern was similar but weaker for mental effort. A cumulative logit model with cross-classified random effects determined that high gamma (90–150Hz) over the LH temporal cortex predicted engagement ratings, while controlling for reaction time and accuracy. However, for effort ratings, reaction time was the sole significant predictor. These results suggest that high gamma may be a correlate of engagement during complex cognitive tasks, but not a correlate of effort. The findings are a promising step toward the goal of objectively measuring engagement during assessment tasks.