Experimental study with random allocation of treatments is regarded as the gold standard for estimation of causal parameters in statistical causal inference. However, when non-compliance among participants exists in the experiment it is likely to result in biased estimates of the parameters of interest. This paper discusses a sensitivity analysis in the estimation of causal parameters under apparent non-compliance. A motivating example is shown that concerns students' performance in university lectures. A procedure of sensitivity analysis for the estimates of causal parameters is presented that incorporates existence of apparent non-compliers, who are genuine compliers but act as non-compliers. An example of such procedure is shown for the case considered.