Prediction of exam performance from information about motivation and ability of students by Indian subjects always supported an adding-type rule. As this rule implies that motivation is equally effective with persons of low through high ability, it may be regarded as reflective of an idealistic philosophy. The present research tested the hypothesis that a multiplying-type rule which implies that motivation is more effective with persons of high than of low ability may be used by Indian subjects if the situation demands realistic estimates. Twenty-four couples expressed expectations from their only-son in easy through difficult exams to school principal confidentially. Predictions by mothers obeyed the multiplying-type rule; those by fathers obeyed the adding-type rule. Exam difficulty changed pattern in father's judgments but not in mother's judgments. However, parents held a similar belief: Effectiveness of motivation increases with sons of high ability but decreases with sons of low ability as difficulty of exam increases. Of the three possible explanations for the effects of exam difficulty, changes in weight of information seemed to be the most parsimonious.