From the following persons who is helping the child/children in his/their…

Intrinsic motivation is the drive to engage in an activity for the internal satisfaction, sense of competence, or interest it provides, rather than for an external reward. Self-determination theory (Deci and Ryan) distinguishes rewards that are informational -- conveying genuine competence or effort without implied pressure -- from those that are controlling, or that make a tangible object contingent on a specific outcome. The contingent, tangible kind tends to trigger the overjustification effect, where effort becomes attributed to the reward rather than to genuine interest.

Here, the son is praised in words for a specific, verifiable result: earning the highest marks in science, with no object, privilege, or future condition attached. Read as information about his own competence rather than as pressure to perform, this achievement-linked verbal feedback is the kind self-determination theory treats as supporting his internally driven interest in the subject.

Contrast with the other actions:

• Chocolates given for behaving properly tie the treat directly to compliance -- a contingent incentive pattern linked to the overjustification effect, where the desired behaviour becomes attached to expecting the treat.

• Story books given specifically because of promotion to the next class make the gift conditional on that one outcome -- the same tangible, outcome-contingent pattern.

• A birthday party marks the calendar occasion of the birthday itself, not any measured skill, effort, or result -- nothing about the celebration is tied to a specific accomplishment.