A reinforcement is any event following a behaviour that strengthens the behaviour and increases the probability of that behaviour occurring again. Reinforcement can be positive or negative.
Some degree of self-discipline is necessary for a child to succeed in school. Positive reinforcement is a useful tool to inculcate self-discipline ... to get some behaviours started and going. In positive reinforcement, a rewarding stimulus is presented immediately after the desired behaviour to increase the probability of that behaviour occurring again. For example, we reward our children with 15 minutes of computer time for completing a piece of homework. If your child likes to play on the computer, he is likely to continue with his next piece of homework.
In the use of reinforcement, we need to ask, "What am I actually reinforcing?" Sometimes, we accidentally reinforce the wrong behaviour. For example, your child cries, "I can't do it" and you promise to buy him a toy if he tries. What you may be reinforcing is the soliciting of rewards. The next time, he is likely to say, "I can't do it" again, and hope that you will promise another toy.
Reinforcements are relative. What may be an attractive reward to one child may not be attractive to another child. We should offer as a reward something that the child desires.
The timing of the reinforcement is important. To be truly effective, give rewards when the desirable behaviour is occurring so as to associate the reward with the behaviour. Therefore, verbal praise or hugs are powerful reinforcements because they can be readily given. Moreover, such reinforcements shift the focus away from material objects to parental affection. With young children, immediate rewards are most effective. As they grow older, children are prepared to wait longer for rewards.
If it is not possible to reward the child immediately, use a conditioned reinforcer. Most parents are familiar with "star charts" with rows and columns where we award stars for certain behaviours. Children accumulate stars up to a certain number to exchange for something that they really want. The stars in this case are conditioned reinforcers.
The number of rows and columns (hence the number of boxes) should vary in proportion to your child's ability to defer gratification. The number of stars (reinforcement) given for a behaviour should be as few as possible to allow for more reinforcements until the behaviour is learned. You do not want your children to fill up the star chart too fast before the desired behaviour becomes a way of life. The number of stars given should also be as many as necessary to keep the reward desirable to the child.
Once the desired behaviour becomes habitual or when the child discovers that the new behaviour is rewarding in its right, switch to a variable schedule of reinforcement (that is, reward on a random or unpredictable basis). If you were to give a surprise reward for reading then your child would read more, hoping for a repeat surprise. A variable schedule of reinforcement will help to keep an already-learned behaviour going. Alternatively, you may want to raise the criteria (in small increments) for earning a star to challenge and make it easy for the child to improve steadily.
Please note that a variable schedule of reinforcement can work against you if you are trying to eliminate an undesirable behaviour. To give in occasionally to a child's whining in the store for a toy will increase the habit of whining whenever he is in a toy shop with you. Consistent ignoring of the undesirable behaviour will extinguish it. However, be prepared for the whining to get louder and longer initially before it begins to decrease and finally disappears.
In negative reinforcement, a desired behaviour is strengthened by the removal of an unpleasant stimulus. An example of shaping behaviour by negative reinforcement is applying something bitter or chilli hot on a pacifier. Out of habit, a toddler puts a pacifier into his mouth but now he experiences something unpleasant. He soon discovers that the unpleasant taste disappears whenever he removes the pacifier from his mouth. Thus the act of removing the pacifier from his mouth is strengthened. This is negative reinforcement.
Suppose your child leaves his clothes on the floor when he knows that he should not ... you call his name and stare at him and then at his clothes on the floor. You continue your look of disapproval until he picks up his clothes. The child experiences relief and you have reinforced his behaviour of picking up his clothes.
Negative reinforcement is especially useful in such situations when the child knows what he should be doing but is doing something else instead. However, negative reinforcement is not effective for active toddlers reaching out for things. Better methods would be putting the objects out of their reach or giving them substitutes to play.