There are times when using rewards are o.k. You can read more here on those. But as a general rule rewards and praise are used too much in the classroom. Or they are used the wrong way. They are generally not an effective means of classroom management. Whether you are teaching English to children or adults these facts will apply. And they will apply to you as well.
Rewards can kill motivation
You don't want to add rewards to something that is intrinsically rewarding already. If it is something that is interesting, fun or enjoyable then adding a reward is a bad idea. If you do your students will lose interest in the activity itself. So if you're doing a drawing activity with your kids you don't need to add a reward. If you are playing a game with your class yo don't need to give stickers to the team that wins.
Here are some activities that are motivating.
Rewards can kill long term interest
If you give your child a $100 every time he gets a 100% on his math exam you might increase his interest in the short term, but kill it in the long term.
Rewards can decrease performance
If you use a reward to get your students to do something their performance is going to decrease. For example, if you tell your kids that there's a pot of gold (stickers, stamps or candy) at the end of the rainbow (let's say their taking a dictation) then it's likely that their writing will be poor.
Rewards can crush creativity
Offering a reward for the completion of a creative project will most likely produce a result that isn't that creative. For example, if we offered a reward to the student who creates the "best" essay and drawing then what we will be doing is stifling the children's creativity. If have the children do the same thing without a reward then you will end up with more creative pieces.
Rewards can encourage cheating
If you use rewards to encourage your students to reach a goal then they are likely to do anything to get there. Which means they may take the "low road" to get there.
Rewards can become addictive
Scientists find that "if-then" motivators resemble drugs with dangerous side effects. So if you say "if" you do this (complete your homework, get an A, etc.) you'll get "this" (stickers, money, candy, etc.) you'll be training them the same way drugs can. Rewards can provide a jolt of dopamine at first and make the student feel good, but it soon disappears and the student will require bigger and better rewards to keep it alive.
Intrinsic rewards are the best
The reward should be the activity itself. When it is then there are no shortcuts because your students will enjoy what they are doing. There may be times when using rewards is o.k, but that is usually just on occasion. Many of these ideas were inspired from the book Drive.