Reward (and punishment) is the most used form of re-enforcement.

Many parents reward their children with 'sweets', time waster toys (including hand-held game devices, mobile phones, computers, etc) and clothes without considering the side-effects like separation time (to play games), distraction from study, access to unhealthy things, and so on.

Perhaps, praise and (self-confident) status (not flattery nor lies) should be given more often than 'materialistic' things.

Like the good doctor says (above): ให้ ความสนใจ ชื่นชม การเรียน และ ผล การเรียนของลูก (my emphasis)